As for me, I subscribe to WoW when a new major content update is released, then play the game all over like a mad man. After a couple months however, I have looted all the current Heroic gear and sets I need and let my sub run out before going back to EVE for the folowing months until the new WoW patch. I usually play MMOs during week days.
Interestingly though, I also hop between Minecraft and Hawken, which I play on the weekends. By default, I am busy constructing my own world projects in MC but whenever a new Hawken mech or map comes out, I set the time aside to grind that new mech all the way to level 25 and fully customize it or master the new map. A couple weekends later, I'm back to Minecraft. Note: probably going to use my Dota 2 beta key and try it out, most likely it will take over all my weekend play time.