I played WoW briefly. I had friends who played it, and I figured I should see what all the fuss was about. So... I started.
I levelled very fast (49 within a few weeks) due to getting lots of advice from wow-related websites, and being given 3 12-slot backpacks by a RL friend when I started. I played a ShadowPriest designed around the principle of face-melting (direct single target damage) and usefulness to my group (healing everyone via VE, using the odd PW:S, casting huge amount of DoTs, etc). I never really did PvP, but I was sorely tempted to do so when anyone told me "priests are for healing, not damage!". That, and the fact I took it too seriously, where what ruined the fun for me.
Most of the people playing seem to be teenagers who don't treat other players with much respect, or even know how to type whole words. The number of single-word requests I got was surprising. "heal?", "rez?", "gold?", "portal?", etc. Mages will understand. You guys always get asked for food and drink... well, priests are the same, except we can get asked for rezzes, heals, buffs, dispels, damage *and* shielding. I actually quite like helping people, but it does annoy me when I'm doing my best to heal a group using VE, and one player seems to think that because my attention is on him, he can use all his best aggro-grabbing abilities and just assume that I will decide to keep him alive. Priests aren't robots. We like to help but there is polite teamwork, and then there is attempting to exploit the priest. It got so bad at one point that I would stay in Shadowform all the time, except when rezzing people to recover from rare wipes. This made it abundantly clear that I could not and would not heal anyone using holy spells. This made some people upset, crying "priests are for healing, not damage!", but I suspect that they were just jealous, as I was usually had the largest DPS output of my group, in addition to doing significant passive healing due to VE.
I enjoyed it a bit, but I tended to treat it took much like a job (as with everything I do). After awhile, I realized that I was spending too much time on WoW, and, while highly successful there, I wasn't giving enough attention to my other projects.
So, I sold everything my account owned, gave the proceeds to my guild as a thank you for helping me, told them I was leaving forever, signed off and set my account not to rebill. Technically I could have come back, but everyone thought I was gone forever, and I had no stuff, so I stuck with it and indeed, never did go back.
I can see how WoW is addicting. If you want to quit as I did, you really need to go cold turkey with it. Sell or give away all your stuff, leave all your guilds, cancel your account, remove all references to WoW from your bookmarks, desktop, friends list, etc. If you only talk to certain people because of WoW, stop talking to them. If you have friends who play WoW a little, ask them not to mention anything WoW-related to you. Physically destroy your WoW CDs and uninstall it from your PC. Do a file search on your hard disk and delete anything related to WoW.
In essence, make sure every trace of it is destroyed from your life.
Have a nice meal to congratulate yourself on starting, then find a new hobby. Preferably one you enjoy but which is unrelated to WoW.
If you've lost a lot of friends from quitting WoW, think about your other hobbies and go to the places where people interested in those other hobbies hang out. This will help you make new friends.
Most of all, look to the future. Have goals. Know what you want out of life. If you don't know what you want, it is easy to get sidetracked on protracted wastes of time like WoW.
If you know what you want, you aren't as prone to wasting time. I've figured out that my RL and OL projects are more important to me than WoW.
You might decide that getting a college place, or graduating University, is more important to you. Whatever it is, find that thing and hang on to it - it will give you the strength to quit WoW when you need to.