I don't think that many people will leave, nobody to my knowledge in my guild that came over from WoW is quitting now, or after the first month. You will always lose people after the first month. A lot of people (myself included) buy every new mmo, expecting that feeling of your virgin mmo. To me that was Lineage 1, to some that was EQ1, or maybe WoW. That feeling of being a part of a world so to speak, for the 1st time. Every mmo, or Diablo 3's, that come out will lose a lot of players after the initial hype.