Do they matter to me????????????
hhhhmmmmmm
My gamercard suggests they do.
Some achievements are clearly over the top. (Perfect dark zero, play 1000 online matches)
But if an achievement is to beat a game on the highest difficulty and you wouldn't normally be brave enough to try that and you succeed, then theres a greater sense of satisfaction knowing you took everything that game could throw at you and survived the onslaught.