The ONLY thing that I've seen achievements do that is positive is encourage a player to play a game from a different approach that they may not have considered before, or promote use of a feature that might otherwise go untouched.

Example: Halo Reach's 1 million score achievement: Yeah, you can cheese it, but maybe, just maybe it encourages you to either A) create your own game type or B) try out the fileshare and download someone else's gametype, and maybe opening your mind to new possibilities.

Sometimes its fun to chase the meaningless number, but I've played plenty of games in the past (when achievements/trophies didn't exist) that simply had a list of challenges to try for the sake of trying or to chase that ever elusive "100% complete" progress bar.

To each, their own.