I've only ever taken a interest in achievments if they have rewarded me with something. Like guns, armour, upgrades, perks, blahblah, you name it. If the achievement offers no reason for me to take it, then undertake it I shall not!
I hope future Rank/Achievement systems offer more rewards to make them worthwhile taking. I don't want to feel I've killed xxx amount of Zombies on L4D2 for a few measly pixels of on-screen text, because that's totally worthwhile! World of Warcraft has a fantastic achievement system, with titles, mounts, gear rewards etc. Achievements = requirements for other achivements, lots of stuff to do and helps get people doing things you would never expect to be doing. Old dungeons etc.
I hate steam and windows live. Both their achievment systems are cr*p and should be removed so I'm not distracted by the pointless achievements popping up in the top right hand of my screen every time I do something absolutely easy and pointless. Woah, shoot 4 zombies in the face with a .44 Magnum. DIFFICULTY!

, yeah having the achievement is awesome, but I have no incentive to do so. If it say, gave me a permament laser sight on all my weapons in multiplayer or something then yea, sure, I'll do it, because I got a reward.
Windows live is good for connecting PC/Xbox 360 users and building some sort of community. I feel steam is the best games release platform yet and I use it only to chat with (via steam friends) and buy and launch my games, adding all my shortcuts makes it painless to hunt for a launcher icon for a game.