I've never been afraid to go on breaks whenever I felt like the game wasn't satisfying. So despite buying it all the way back in 2005, I think I "only" have about 2 years worth of active subscriptions. My breaks are getting increasingly longer though, and I think I've reached the point where I'm not sure if I'll ever go back.
The main problem I have with WoW in its current state is the lore. This might sound strange to most but I actually got into WoW originally because I really liked the setting in the RTS games. In Cataclysm, I think it shows that the remaining plot lines from Warcraft III have dried out and so far they have failed to keep me interested in the story they are trying to tell. I'm also sick to death of Old Gods, it has become too convenient to blame everything that goes wrong on them. I also find Deathwing to be a boring villain so far, even as a long-time lore fan he strikes me as being just "that dragon boss" with no characterisation beyond the fact that he's crazy. As for the areas, some of them are more concerned about making pop culture references every other minute than actually trying to fit in the setting (see Uldum).
And thanks to the new unlimited trial, if I ever get nostalgic I should be able to get my fit by leveling a character to 20. So at this point in time, I think it would take something quite significant to get me to subscribe again. It does make me sad somewhat because I honestly have a lot of great memories from this game and I often wish I could erase all of it from my memory and start from scratch again.