You guys shouldn't worry about this too much, Achievements have been getting raped for a while. With achievements they reset your GamerScore to 0 and block you from getting any achievements you already had. They will also label you a "cheater" so the entire world can see.
This only happens if people get "Online" achievements with no date stamp (when offline), or if the achievements are screwed up (you unlock the last achievement before the first one, things like that). People can still do it if they're smart about it.
Sony can implement something similar, and that's probably what they're working on now.
I'm more worried about the online cheating, because I don't really know how Sony handles that. Xbox Live is set-up better for this, and people still get away with it. Someone can be a famous hacker with vids all over youtube and they still don't get banned.