Sadly for me, MMO's tend to be an addiction that is only beaten by another, potentially WORSE addiction.
For example.. my addiction to UO (ultima online for the uninitiated) was only defeated by my Everquest Addiction. My Everquest addiction was ultimately overcome by my DOAC (dark age of camelot) addiction, which succumbed itself to my Anarchy Online addiction (anyone remember THAT game??) which eventually fell to the wayside during my Disgaea addiction (which was technically not an MMO and the only time i weened myself away completely. Then Final Fantasy Online eventually took over for a LONG time my life, and then came World of Warcraft which has been the mainstay.
I have yet to find any game to curb my WoW addiction, even though Age of COnan and LOTRO had a good little run... I think the problem is that WoW is MEGA-SOCIAL, meaning that just about anyone and everyone I care to associate with are playing that game with some level of consistency, so it feels just way too natural to slide back into the endless grind while cracking Chuck norris vs. Jason David Franks jokes in the Barrens and bragging about how many stacks of potentially expensive whatever it is we have in the bank.
Sadly it even effects my regular gaming. I have literally HUNDREDS of game worlds hanging in the balance because I played them then went back to wow and never went back to resolve those universes that are still waiting for the destined hero (aka ME) to save them from the evil alien empire, zombies, gangsters, invading army, corrupted lifestream, ancient evil or whatever.