I quit my WoW addiction back in March. Almost 1 year clean. IT got to the point where after 60, unless you just PVP, the only thing to do is get in a good guild and raid high end instances. We were doing BWL, AQ, and MC/ONY runs 4 nights a week. And since I'm on east coast, and we had to give the west coasters enough time to get home from work and stuff, the raid group didn't start forming till 9pm. We'd head out at 10pm and run the instances till 1 or 2am. Doing that 4 nights a week along with getting up for work at 6am simply wore me down. After a few months, I just had enough, and quit. Don't get me wrong, I loved the game, really miss playing my l33t hunter, but I just couldn't support my rock and raid lifestyle anymore.
I thought about picking up burning crusade cause it would offer some more casual content and leveling for me to do, but decided* against it.
* - JJ would rip my nuts off and shove them down my throat if I started playing WoW again.