Today's Gamers MMO Focus Report by Gamesindustry.com and TNS. The report claims that the MMO market in the US has reached 46 million users, with 21 million paying for online games. The rest play without spending a dime (think "freemium").
In a shocking upset victory dripping in sarcasm, World of Warcraft was the most popular MMO with the US, besting NeoPets, Club Penguin, Disney ToonTown and Runescape. Ah freemium, where even the traditional MMO companies can make money.
[Via Massively, Gamasutra]