There's no doubt that WoW is, for the most part, a brilliantly designed game. New players are eased so gradually into the "grinding treadmill" that they're desensitized to the addictive monotony of killing mob after mob for their XP bar to fill in sliver by sliver.
But don't let that make you, uh, forget about real life. It's well and good to spend one, two, or even more hours straight playing WoW, so long as it isn't at the expense of other, real-life needs. And regardless of how free your schedule is, for the sake of your health, it'd be beneficial to take breaks from the game every now and then. For every ten miles your in-game alter ego runs, resolve to run one yourself.
Breaks from WoW make you appreciate the game even more when you come back. Trust me. With 3 70s and a 59 twink, I've obviously spent what most would deem an unhealthy amount of time in Azeroth. And even I tire of farming, grinding, and PvPing every now and then. If I don't step away from the keyboard and spend a few days doing something else, the game would probably start getting to me, and I'd quit.
(A personal anecdote: You know you play too much WoW when someone asks your opinion of a professor, and you respond, "He's lev...levity in a turbulent society" to cover up the fact that you were about to say, "he's Level 70". Yeah...I didn't log in for a solid week after that one.)
See you all in Outland...just not every day, I hope!