Wow some people are just so close minded. As Zlejedi mentioned, there's no downside to achievements, but it adds to the experience. And anything that adds to the experience is a good thing. If you don't like it, just don't pay any heed to them and play your game like you normally play.
I think achievements are great, they make me do insane stuff that sometimes I probably would have never attempted. Like take a different approach or learn a different tactic to tackle a ridiculously hard challenge which actually made me get better at the game.
Also this may not be much, but if you see a guy with 20000 gamer points, you know he has played a pretty wide variety of games or has invested a lot of time in his games as opposed to someone who has 2000 gamer points, who probably hasn't done either of the above.
