If you render the world on zoom level 16, there are 67 million "meta tiles" (each covering an area of 8x8 tiles). The majority of them are in the sea, obviously, and unlikely to have any data. 20 million meta tiles are not in the sea; of these, 4.4 million have at least one node.
As of 27th May 2012, only 142 of these meta tiles have more than 100,000 nodes on them; the front-runner has a whopping 227,000. (105 are in France, 26 in the US, 3 each in Italy and Brazil, and one each in Spain, Japan, Denmark, Austria, and Indonesia.) Here is the list of those top 142 areas.
142. Antony, Hauts-de-Seine, Île-de-France, 92160, France (100027 nodes)
141. 広尾 (Hiroo), Tokyo, 東京都 (Tokyo), Tokyo Metropolis, Kanto Region, Japan (100317 nodes)
140. Sauganash, Cook, Illinois, United States of America (100513 nodes)
139. Yerres, Évry, Essonne, Île-de-France, 91330, France (100603 nodes)
138. Les Hauts de Chatou, Chatou, Saint-Germain-en-Laye, Yvelines, Île-de-France, 78400, France (101214 nodes)
137. Vigneux-sur-Seine, Évry, Essonne, Île-de-France, 91270, France (101444 nodes)
136. Greenacres, Kern County, California, United States of America (101467 nodes)
135. Carcassonne, Aude, Languedoc-Roussillon, 11000, France (101699 nodes)
134. Le Tremblay, Champigny-sur-Marne, Nogent-sur-Marne, Val-de-Marne, Île-de-France, France (101783 nodes)
133. Søndervang, Kolding, Kolding Kommune, Region Syddanmark, Denmark (101931 nodes)
132. Cyprian, Villeurbanne, Lyon, Rhône, Rhône-Alpes, France (101961 nodes)
131. Baie-Mahault, Basse-Terre, Guadeloupe (102450 nodes)
130. Will-O-Dean Acres, Wake, North Carolina, United States of America (102661 nodes)
129. Pôle de proximité Loire et Sèvre, Nantes, Loire-Atlantique, Pays de la Loire, France (102883 nodes)
128. Meudon-la-Forêt, Meudon, Boulogne-Billancourt, Hauts-de-Seine, Île-de-France, 92360, France (103788 nodes)
127. Laubadère, Tarbes, Hautes-Pyrénées, Midi-Pyrénées, France (104120 nodes)
126. Lille, Nord, Nord-Pas-de-Calais, 59000, France (104277 nodes)
125. Bologna, Emilia-Romagna, Italy (104294 nodes)
124. Plateau d'Avron, Neuilly-Plaisance, Le Raincy, Seine-Saint-Denis, Île-de-France, France (104375 nodes)
123. Reims, Marne, Champagne-Ardenne, 51100, France (104448 nodes)
122. Região Administrativa VI - Continente, Vitória, Microregião Vitória, Greater Vitória, Mesaregião Central Espírito-Santense, Espírito Santo, Brazil (104607 nodes)
121. Les Cévennes, Montpellier, Hérault, Languedoc-Roussillon, France (104874 nodes)
120. Pôle de proximité de l'Aubinière, Thouaré-sur-Loire, Nantes, Loire-Atlantique, Pays de la Loire, France (104903 nodes)
119. Mont-Saint-Aignan, Seine-Maritime, Haute-Normandie, 76130, France (104950 nodes)
118. Lyon 3e Arrondissement, Lyon, Rhône, Rhône-Alpes, 69003, France (105310 nodes)
117. Pôle de proximité Nantes-Loire, Nantes, Loire-Atlantique, Pays de la Loire, France (105429 nodes)
116. Les Hauts de Chatou, Chatou, Saint-Germain-en-Laye, Yvelines, Île-de-France, 78400, France (105810 nodes)
115. Bobigny, Seine-Saint-Denis, Île-de-France, 93000, France (106024 nodes)
114. Franckviertel, Gemeinde Linz (Stadt), Bezirk Linz (Stadt), Linz, Upper Austria, Austria (106617 nodes)
113. La Closerie du Plessis, Le Plessis-Bouchard, Pontoise, Val-d'Oise, Île-de-France, France (107221 nodes)
112. Kern, Kern County, California, United States of America (107465 nodes)
111. Nice, Alpes-Maritimes, Provence-Alpes-Côte-d'Azur, 06000, France (107790 nodes)
110. Marseille 10e Arrondissement, Marseille, Bouches-du-Rhône, Provence-Alpes-Côte-d'Azur, 13010, France (107866 nodes)
109. Sannois, Argenteuil, Val-d'Oise, Île-de-France, 95110, France (108290 nodes)
108. Camp Rambeaud, Le Pontet, Avignon, Vaucluse, Provence-Alpes-Côte-d'Azur, France (108743 nodes)
107. Pôle de proximité Nantes-Ouest, Nantes, Loire-Atlantique, Pays de la Loire, France (108791 nodes)
106. Limoges, Haute-Vienne, Limousin, 87000, France (108971 nodes)
105. Prés d'Arènes, Montpellier, Hérault, Languedoc-Roussillon, France (109105 nodes)
104. Bois-Guillaume-Bihorel, Seine-Maritime, Haute-Normandie, 76230, France (109311 nodes)
103. Decatur, DeKalb County, Georgia, United States of America (109980 nodes)
102. Peoria, Illinois, United States of America, North America (110001 nodes)
101. 16th Arrondissement, Paris, Île-de-France, 75016;75116, France, Europe (110411 nodes)
100. Le Grand Louis, Mérignac, Bordeaux, Gironde, Aquitaine, France (110444 nodes)
99. Marseille 13e Arrondissement, Marseille, Bouches-du-Rhône, Provence-Alpes-Côte-d'Azur, 13013, France (110866 nodes)
98. Plateau d'Avron, Neuilly-Plaisance, Le Raincy, Seine-Saint-Denis, Île-de-France, France (111129 nodes)
97. Savigny-sur-Orge, Palaiseau, Essonne, Île-de-France, 91600, France (111481 nodes)
96. Royan, Rochefort, Charente-Maritime, Poitou-Charentes, 17200, France (111769 nodes)
95. Pau, Pyrénées-Atlantiques, Aquitaine, 64000, France (111969 nodes)
94. Tourcoing, Lille, Nord, Nord-Pas-de-Calais, 59200, France (112598 nodes)
93. Poitiers, Vienne, Poitou-Charentes, 86000, France (112602 nodes)
92. Les Luats, Villiers-sur-Marne, Nogent-sur-Marne, Val-de-Marne, Île-de-France, France (112687 nodes)
91. Enghien-les-Bains, Sarcelles, Val-d'Oise, Île-de-France, 95880, France (112690 nodes)
90. 3, Toulouse, Haute-Garonne, Midi-Pyrénées, France (112873 nodes)
89. Krutenau, Strasbourg, Strasbourg - Ville, Bas-Rhin, Alsace, France (113371 nodes)
88. Borgo Mestre, Treviso, Veneto, Italy (113806 nodes)
87. Angoulême, Charente, Poitou-Charentes, 16000, France (113919 nodes)
86. Wible Orchard, Kern County, California, United States of America (114941 nodes)
85. Plateau d'Avron, Neuilly-Plaisance, Le Raincy, Seine-Saint-Denis, Île-de-France, France (115025 nodes)
84. Le Bourget, Bobigny, Seine-Saint-Denis, Île-de-France, 93350, France (115593 nodes)
83. Pôle de proximité Loire et Sèvre, Nantes, Loire-Atlantique, Pays de la Loire, France (115810 nodes)
82. Sevran, Le Raincy, Seine-Saint-Denis, Île-de-France, 93270, France (115876 nodes)
81. West Elsdon, Cook, Illinois, United States of America (115959 nodes)
80. Arcella, Padova, Veneto, Italy (116463 nodes)
79. Le Plateau, Sartrouville, Saint-Germain-en-Laye, Yvelines, Île-de-France, France (116602 nodes)
78. La Roche-sur-Yon, Vendée, Pays de la Loire, 85000, France (116865 nodes)
77. Aplemont, Le Havre, Seine-Maritime, Haute-Normandie, France (117933 nodes)
76. Le Plateau, Sartrouville, Saint-Germain-en-Laye, Yvelines, Île-de-France, France (118446 nodes)
75. Belcier, Bordeaux, Gironde, Aquitaine, France (118688 nodes)
74. Croix d'Argent, Montpellier, Hérault, Languedoc-Roussillon, France (119447 nodes)
73. Clearing, Cook, Illinois, United States of America (119867 nodes)
72. Cabirol, Colomiers, Toulouse, Haute-Garonne, Midi-Pyrénées, France (120524 nodes)
71. Chapel Hill, Orange, North Carolina, United States of America (120624 nodes)
70. Raleigh, Durham, North Carolina, United States of America (120778 nodes)
69. Val d'Egout, Toulon, Var, Provence-Alpes-Côte-d'Azur, France (120778 nodes)
68. Clermont-Ferrand, Puy-de-Dôme, Auvergne, 63000, France (121496 nodes)
67. 13th Arrondissement, Paris, Île-de-France, 75013, France, Europe (122969 nodes)
66. Flers Neuf, Villeneuve-d'Ascq, Lille, Nord, Nord-Pas-de-Calais, France (123413 nodes)
65. Bagneux, Antony, Hauts-de-Seine, Île-de-France, 92220, France (124063 nodes)
64. Villejuif, L'Haÿ-les-Roses, Val-de-Marne, Île-de-France, 94800, France (124455 nodes)
63. Carrboro, Orange, North Carolina, United States of America (124749 nodes)
62. Raleigh, Durham, North Carolina, United States of America (126626 nodes)
61. Béziers, Hérault, Languedoc-Roussillon, 34500, France (127686 nodes)
60. Le Capreau, Wasquehal, Lille, Nord, Nord-Pas-de-Calais, France (128693 nodes)
59. Bakersfield, Kern County, California, United States of America, North America (128759 nodes)
58. Girona, Catalunya, Spain (129684 nodes)
57. Calais, Pas-de-Calais, Nord-Pas-de-Calais, 62100, France (129867 nodes)
56. Le Tampon, Saint-Pierre, La Réunion (129871 nodes)
55. Amiens, Somme, Picardie, 80000, France (130476 nodes)
54. Les Olives, Marseille 13e Arrondissement, Marseille, Bouches-du-Rhône, Provence-Alpes-Côte-d'Azur, France (131441 nodes)
53. Hôpitaux-Facultés, Montpellier, Hérault, Languedoc-Roussillon, France (132118 nodes)
52. Cholette, Niort, Deux-Sèvres, Poitou-Charentes, France (133409 nodes)
51. Georgetown, Washington, Fairfax (city), District of Columbia, United States of America (134116 nodes)
50. Prébendes, Tours, Indre-et-Loire, Centre, France (134394 nodes)
49. 19th Arrondissement, Paris, Île-de-France, 75019, France, Europe (134409 nodes)
48. Hempempont, Villeneuve-d'Ascq, Lille, Nord, Nord-Pas-de-Calais, France (134769 nodes)
47. East Garfield Park, Cook, Illinois, United States of America (134977 nodes)
46. Bakersfield, Kern County, California, United States of America, North America (135304 nodes)
45. Troyes, Aube, Champagne-Ardenne, 10600, France (136075 nodes)
44. Dijon, Côte-d'Or, Bourgogne, 21000, France (136080 nodes)
43. 11th Arrondissement, Paris, Île-de-France, 75011, France, Europe (137172 nodes)
42. Pôle de proximité Nantes-Ouest, Nantes, Loire-Atlantique, Pays de la Loire, France (138430 nodes)
41. Gladstone, Cook, Illinois, United States of America (139797 nodes)
40. Suresnes, Nanterre, Hauts-de-Seine, Île-de-France, 92150, France (140169 nodes)
39. Angers, Maine-et-Loire, Pays de la Loire, 49000, France (140744 nodes)
38. Le Blanc-Mesnil, Le Raincy, Seine-Saint-Denis, Île-de-France, 93150, France (140830 nodes)
37. L'Aiguillon, Toulon, Var, Provence-Alpes-Côte-d'Azur, France (141582 nodes)
36. Cleveland Park, Washington, Montgomery, District of Columbia, United States of America (142047 nodes)
35. Simpang Haru, Cirebon, Indonesia (143084 nodes)
34. Plateau d'Avron, Neuilly-Plaisance, Le Raincy, Seine-Saint-Denis, Île-de-France, France (143406 nodes)
33. Vincennes, Nogent-sur-Marne, Val-de-Marne, Île-de-France, 94300, France (143491 nodes)
32. Malakoff, Antony, Hauts-de-Seine, Île-de-France, 92240, France (145038 nodes)
31. Rouen, Seine-Maritime, Haute-Normandie, 76000, France (145690 nodes)
30. Quailwood, Kern County, California, United States of America (146834 nodes)
29. Hanson Park, Cook, Illinois, United States of America (147428 nodes)
28. 2, Toulouse, Haute-Garonne, Midi-Pyrénées, France (147428 nodes)
27. Plateau d'Avron, Neuilly-Plaisance, Le Raincy, Seine-Saint-Denis, Île-de-France, France (148322 nodes)
26. Romainville, Bobigny, Seine-Saint-Denis, Île-de-France, 93230, France (149254 nodes)
25. 4, Toulouse, Haute-Garonne, Midi-Pyrénées, France (150387 nodes)
24. Centro, Vila Velha, Microregião Vitória, Greater Vitória, Mesaregião Central Espírito-Santense, Espírito Santo, Brazil (150544 nodes)
23. Hautes Vallergues, Cannes, Grasse, Alpes-Maritimes, Provence-Alpes-Côte-d'Azur, France (150755 nodes)
22. Le Moufia, Saint-Denis, La Réunion (153539 nodes)
21. Willow Creek, Wake, North Carolina, United States of America (153771 nodes)
20. Mount Vernon Square, Washington, Montgomery, District of Columbia, United States of America (154385 nodes)
19. Les Bruyères, Sèvres, Boulogne-Billancourt, Hauts-de-Seine, Île-de-France, France (154783 nodes)
18. Bois Cadet, Montesquieu, Fontenay-sous-Bois, Nogent-sur-Marne, Val-de-Marne, Île-de-France, France (154875 nodes)
17. 7th Arrondissement, Paris, Île-de-France, 75007, France, Europe (156704 nodes)
16. Marseille 3e Arrondissement, Marseille, Bouches-du-Rhône, Provence-Alpes-Côte-d'Azur, 13003, France (160887 nodes)
15. Schorsch, Cook, Illinois, United States of America (161129 nodes)
14. Marseille 12e Arrondissement, Marseille, Bouches-du-Rhône, Provence-Alpes-Côte-d'Azur, 13012, France (165281 nodes)
13. Sanvic, Le Havre, Seine-Maritime, Haute-Normandie, France (166744 nodes)
12. 5th Arrondissement, Paris, Île-de-France, 75005, France, Europe (171368 nodes)
11. Irving Park, Cook, Illinois, United States of America (175352 nodes)
10. Hermosa, Cook, Illinois, United States of America (175815 nodes)
9. Marseille 8e Arrondissement, Marseille, Bouches-du-Rhône, Provence-Alpes-Côte-d'Azur, 13008, France (178263 nodes)
8. Le Mans, Sarthe, Pays de la Loire, 72000, France (181766 nodes)
7. 8th Arrondissement, Paris, Île-de-France, 75008, France, Europe (187994 nodes)
6. 10th Arrondissement, Paris, Île-de-France, 75010, France, Europe (188034 nodes)
5. St-Augustin - Quintin-Loucheur - Tondu, Bordeaux, Gironde, Aquitaine, France (191899 nodes)
4. Bois-Colombes, Nanterre, Hauts-de-Seine, Île-de-France, 92270, France (195964 nodes)
3. Fondaudège, Bordeaux, Gironde, Aquitaine, France (212188 nodes)
2. Região Administrativa IV - Maruípe, Vitória, Microregião Vitória, Greater Vitória, Mesaregião Central Espírito-Santense, Espírito Santo, Brazil (224476 nodes)
1. Morne Desaix, Fort-de-France (227543 nodes)