I've been on and off since Cata. Quit for most of MoP, came back before right near the end of it only because I wanted to kill Garrosh and get my legendary cloak while I still had the chance. Then played a month of WoD before I quit again because I was bored with garrisons. I'm interested in coming back for 6.2 though depending on how good Tanaan Jungle/Hellfire Citadel looks, also Mythic dungeons sound fun.
Stopped playing for good in MoP after SoO. I would have stopped after the first raids in Cata were done but I got involved in PvP and achievments. The PvP aspect of the game was turned to shit in MoP, and after the raid content was on farm the game just lost all appeal.
started in Vanilla when AQ was being released, first left in WotLK, like, 2 weeks before dual-specs and unique druid forms came out [serious rage ensues]. came back in Cata and was sent into a furious rage about LFR. been out since then.