Free to Play -- when will this take hold on the major MMO market?

Free to play "MMOs" have been around for quite a while, but Dungeon and Dragon's is the first of what I would consider to be a major MMO to adopt that model. It was apparently a good business decision for them--at least player wise, though I would be interested to see how profitable this is for Turbine. Especially with the current legal machinations between Turbine and Atari.