There is a lovely articaly on GameDaily Biz today, titled Microsoft's Achievement Points Yield 'Nerd Cred' http://biz.gamedaily.com/industry/feature/?id=14866
I couldn't agree more. I don't want to sound like I'm trying to sell 360s here, but I would say for me achievements are the #1 thing I love about my X-Box. Those who know me can easily attest to my being an achievement whore. Not nessecarily to get 'cred', but the feeling of accomplishment.
While we are on the subject of achievements, I'll give a quick shout-out to two great achievement-related sites.http://www.xbox360achievements.org/home/http://www.mygamercard.net/
And, in case you were interested here is my GamerCard. As it turns out no, I am not a real 16FCheerleader. The handle comes from back in the day when I played Counter-Strike at LAN parties in high school. You can't help but giggle when you see messages like "Bob was headshoted by A16FCheerleader", so the handle kind of stuck after that.