I played WoW from closed Beta to 2days ago. I quit multiple times for the max duration of 1 week. I ran MC, Ony, and BWL, Non stop never missed a raid, I pvp'ed little and grinded rep. I didn't mind the raiding since we had a good guild and the people kind of made the game. When you hit 60, you have 2 choices. Grind all the epics in all end game instances and play the World of Repcraft like they designed it, or you can quit the game and say hey, I like my job and my grades.
I was an officer of the guild, I lead raids, I was one of the best geared in the guild. What you need to do to quit, is to think of where you thought you were going to be before you started playing. Has your playing interrupted the future that you had imagined. If the answer is yes, then you need to sell your account and use the money on your future.
My story as it is happening right now. I was supposed to graduate last fall, I played the game for over a year, I only completed 2 classes a semester as opposed to my usual load of 5classes. I didn't lose my GF, I didn't lose my Job, but I lost a good chunk of my lofty GPA. I had to pay extra for classes since I was repeating them.
Its not so much that you enjoy playing the game, but if you feel guilty doing it, then you should quit.
OPPORTUNITY COST
The true cost of something is what you give up to get it. This includes not only the money spent in buying (or doing) the something, but also the economic benefits (UTILITY) that you did without because you bought (or did) that particular something and thus can no longer buy (or do) something else. For example, the opportunity cost of choosing to train as a lawyer is not merely the tuition fees, PRICE of books, and so on, but also the fact that you are no longer able to spend your time holding down a salaried job or developing your skills as a footballer. These lost opportunities may represent a significant loss of utility. Going for a walk may appear to cost nothing, until you consider the opportunity forgone to use that time earning money. Everything you do has an opportunity cost (see SHADOW PRICE). ECONOMICS is primarily about the efficient use of scarce resources, and the notion of opportunity cost plays a crucial part in ensuring that resources are indeed being used efficiently.