Of course, that's if you count Neopets. Which I guess you should. Sigh.
There's an article on Smart Mobs which claims that there are more game avatars than people in the USA right now.
The more avatars than Americans stat is one of many things I learned about the 3D Net edge by spending two days last week at Virtual Worlds 2008 in New York. Avatar mobbing is virtually here for sure. A keynote by Barbiegirls.com described the girls virtual world sensation, where 11 million are signed up and thousands more join every day. Another huge virtual world toy phenomenon is neopets, where the toy in a childs hand has a virtual life online. The virtual world of gaming also contributes huge portions of the avatar population.
Read all about it at Smart Mobs.