Im really not sure whether AdventureQuest was an MMO (I think it is now), but I can still remember the day I realized the entirety of that game was just pressing "Attack" for hours on end.
I then moved on to RuneScape, enjoyed it for a while, but then I discovered WoW.
I thought, "OMG INCREDIBLE GRAPHIXX MUST PLAY NOAW!", and moved to WoW.
After 2 realm changes and... 3 character adjustments, I was put off by Cataclysm - it felt like Blizzard were charging for content that I should already be getting (C'mon Blizz, I already pay £45 twice a year...).
So now I'm withought a good MMO. I have a horrible feeling that one day WoW will wrap it's tendrils round my feeble mind once more and I'll carry on paying far too much for the same grinding... but at least my gear will be pretty :>