The fastest selling Capcom game is now Monster Hunter Freedom 3, or Monster Hunter Portable 3rd for you Westerners. The PSP title flew off shelves in Japan, selling 3 million copies in 17 days, breaking records for Capcom and the entire industry in Japan. That takes the series total up to about 16 million.
It makes sense that PSP system sales are also up. Eurogamer says that the PSP sales numbers shot up from 75,000 to 325,000 on MHF3's launch week.
Stats like these show that Japan is a completely different market than here in the US. Monster Hunter is a small club here, and PSP owners are always on the defensive.