The sales are quite insane. For a comparison, Pokemon Diamond/Pearl sold 2.6 million in its first 4 weeks. Diamond/Pearl ended up selling 6 million in Japan, and become the 5th best selling game ever there.
Black/White should end somewhere around there too. That will make the top 7 best-selling games in Japan all either Pokemon or Mario. It will also make the DS have 6 of the top 10 best selling games there.
Someone brought up a question about the biggest franchises. Pokemon is nowhere near Mario. But again, nothing is anywhere near Pokemon either. Unless you count the Wii series. Don't shoot me if I forgot anything.
1. Mario - 416.5 million
2. Pokemon - 194 million
3. Grand Theft Auto - 87 million
4. Final Fantasy - 84 million
5. Sonic - 75 million
6. Call of Duty - 68 million
Zelda - 60 million
It's a short list, because I'm really just illustrating a point with the top 3.