I don't care about them much, especially not Steam achievements that doesn't count towards some greater general score, but at the same time I can't deny they sometimes made me do things I wouldn't usually do or even think of. Like the golf club achievement in Bioshock 2.
Also, the very first thing I did when I got a PS3 about a year ago, was to get the platinum trophy in Mirror's Edge. I had played the PC version of the game lots and lots, which doesn't have any achievements, and I thought that if the PC version had achievements, I would have taken them all for sure. And then just to prove that to myself, I took them all right away on the PS3 as soon as I could, which didn't really take that long. 8-9 hours or so, I guess.
But that's the only PS3 game I've bothered to get all trophies with, in general I don't really care about them. Seems like only a select few games are worthy about becoming a personal achievement/trophy goal
