PlayDevil has posted a short but interesting article on the subject "Achievements tainting gaming ?".
Here's a snip:
"Essentially the gamerscore situation is brilliant and gets me playing games I would not have touched previously however it's got to the point where I would purposely not buy a game if I didn't receive an award for playing, prime examples of this are related to PS3 / PC games. Now my PC doesn't get a lot of use for games anyway as I've kind of broke away from that scene but in the terms of the PS3 I will not get a game unless it has the trophies attached to it (or of course it has an outstanding review). Example of this is for Metal Gear Solid 4, I've been putting off the purchase in the hope of trophies being introduced at a later date."