Some interesting results. First, less than 57% (through 154 votes) are switching to 4e. That seems relatively small, and probably smaller than Wizards would like. Now given that EN World isn't entirely exemplary of the entire gaming populace--it has a lower percentage of "casual gamers"--we could probably bump that number up a bit. But maybe not? And isn't there less of an exodus this time around than last time? I mean on one hand, 4e is selling extremely well by all accounts, on the other it seems there is a lot of resistance to it, a lot of "meh." So it may be that while a lot of folks are BUYING it, less people will switch to PLAYING it.
I don't know where this figure came from as there is no citation, but according to Wikipedia "There are an estimated 5.5 million regular players of all editions of D&D, with the majority of those players (roughly 4 million) playing the most recent edition." If 4 of 5.5 million play 3.x, which is 73%. We could have that a range and say that between 65-80% of all D&D players play(ed) 3e. It will be interesting to see if that percentage drops for 4e, perhaps partially because of the success of 3.x.
It is also interesting to note just how many folks have been "Left Behind" with previous editions (I know, I know--it is a conscious choice, but I just wanted to use "Left Behind"

). To some degree I think people just get comfortable with a system, or perhaps after a hiatus from gaming and/or D&D, want to return to their old books because of nostalgia.