And from January 2011 the announcement of the country quotas:

Australia 181
Austria 32
Belgium 114
Canada 130
Denmark 182
France 2413
Germany 388
Great-Britain 385
Italia 351
Japan 288
Netherlands 82
Russia 83
Spain 198
Sweden 112
Switzerland 33
USA 719
Other countries 309

Total 6000

Additional information on the registration info page on the PBP site.

The increase to 6000 rider will be accomodated in part by adding a sleeping facility after Loudeac:

Start times & new sleep control after Loudeac
Youtube interview with Jean-Gualbert Faburel