My opinion on F2P is that it creates a weak community. You have players who aren't invested in the game. You'll have much more unique users, much fewer dedicated players.
This is what I think happens with F2P. There may be a F2P MMO that comes along and proves this wrong, but I haven't seen it yet. I'd rather play with a smaller number of dedicated players, people you see day in and day out, than have a larger population initially that end up walking away in favor of something else. If you don't have to pay a monthly fee, the achievements, friendships, and time you put into your character in that game have less of a value in my opinion and are easier to abandon.