Achivements can move up to 40,000 copies of a game.

[Kantor]

thekitchensink said:
Well, I know that, all other things being equal, I tend to choose the 360 version because I prefer Achievements to Trophies. Like with Arkham Asylum, if the PS3 didn't have the extra content, I'd have got it on the 360.

I don't understand when people say this. They are the same thing! The only difference is that one is a number and one is an icon. The actual "achievement", ie the thing you do to get that number/icon, is the same. That should really be the most important part, the feeling of knowing you have done it, rather than the visual feedback given.