I made the decision some time ago, shortly after reaching level 70 actually. I cancelled my account, but decided as it didnt end till today, I would play out my remaining time to see A) did I make the right decision, and B) can I explain my decision to quit the game. Now, the answer to both questions is yes.
I want to start out by saying I love my guild. They are pretty much entirely the reason I stuck with the game in the first place. Previously in playing I got stuck at level 40 saying "now what?", and normally the answer was to just roll up another alt. Everyone in our guild is helpful and knowledgable, it is a great environment. I also feel like the guild membership helped me get better in my own skills. I learned marking and kill order from watching people in our guild do it. Our guild was definately NOT a reason for me leaving.
I've been thinking about it some time, and I basically have 2 reasons for leaving: PvP and grinding. I despise PvP. I don't like battegrounds, I don't like arena, and I definately don't like some douchebag ganking me while I'm going about my own business. I dislike this to a degree where I had considered quitting the game months ago, and it is the reason why I left for Azuremyst in the first place. I don't see this improving in WOTLK, in fact I see it getting worse. As my main character is a protection paladin, I simply don't have the tools to defend myself. Not that it really matters. Even if I was a PvP god and could kill any person who took up arms against me, it would still be time wasted when I could otherwise be doing something else.
How do you take the slaughter of hundreds of enemies using massively powerful and cool to look at abilities and make it not only not fun, but tedious and boring? You make it a means and not an end. I'll give you an example. One of my goals before I quit the game was to solo Black Rock Depths. Tons of mobs, I figured it would be fun. I got lost a lot and it took a long time, but I did it. I ended up getting about 200 runecloth and as I had a tailor, I figured it would be a good way to get runecloth to make runcloth belts to disenchant to get dream dust to level enchanting (this is how I think, characters provide for my other characters, cut out the middle man, cheap and efficient). When it changed from "I want to kill all these guys because I am powerful and I can" to "I need to kill these guys to harvest runecloth", it became tedious and not fun. The act was the same, the goal was not. Basically, from what I've seen, the game after you hit level 70 is a grind. You get to pick what you grind, instances for gear, mobs to get reputation to get gear, or gold to raise professions to get gear, but its still a grind, and grinds aren't fun. I LOVE AOE killing. But I like it because its an option, not because I have to do it.
So in summary I know why I quit, and I don't see either situation improving. WotLK will still have an endgame, and this endgame will still require grinding. It may extend the time between grinding, but it will still be an issue. Secondly, my entire guild is not going to pick up and move to a PvE server, and blizzard is not going to say "you know, prot paladins should be able to reflect ranged and spell damage too, so they can just stand there and pwn n00bz in Pvp". As I don't see either of these conditions changing, whether I quit the game now or quit later, the end result is the same. Doing it now just saves me the money on the monthly fee and buying the expansion.
Mid Afternoon Quickie
2 years ago