Hm. Roughly 40%, I guess.

And that 40% would be overwhelmingly Pathfinder, or a house-ruled variant thereof.
None of the rest is 4e - not even the gamers that the gamers I know, know.

The vast majority of the remainder is in fact totally non-D&D.
But the thing is, it's a variable ratio. This is only a snapshot. At times, the entire "extended family"

has been mostly D&D (and/or D&D-ish), for example.
Note: I mightn't have seen this poll for some time,
if at all, if it hadn't been visible from the main forum page, as it was just now. Would it be a better idea to run it in the general RPG forum, and make it so that voters' usernames show up? That would be my choice, anyway.