While there are only about 20 posts so far I find it interesting that the majority of responses are one of two general answers: "No one but me" or "Almost everyone." Where's the middle ground? Why isn't anyone (or almost no one) saying "about half."
I'm in the former category. Of my group of eight, only one other guy (my co-DM) has heard of EN World as far as I can tell--I don't think he has a login, though.
My guess is that the majority of ENWorlders (or RPGNetters) are of the same category; those that aren't, well, maybe they play together?

But this goes along with my view that you can categorize gamers into three general types based upon how into RPGs they are: Casual, Serious, and Hardcore. If you are reading this right now you are at least "Serious": You think about RPGs on a regular, probably daily, basis, you have more books than you actually use, and you play--or want to play--in a regular game. You've also almost certainly GMed.
The ratio is probably something like 100:10:1, maybe even something like 500:10:1. So if there are a million active D&D players in the US right now there are probably about 20,000 "serious" gamers, and 1-2,000 "hardcore" gamers. This is why, I think, it seems like there are barely any gamers--because there aren't a lot of serious-to-hardcore gamers; the bulk of the D&D playing populace shows up for their once-every-other-week game and doesn't think about it much in-between sessions.