I am Nick Yee. I study gamers for a living. Have surveyed over 55,000 MMO players, analyzed server-side data from WoW, and currently work for a game company. AMA.
Update: Thanks for all the thoughtful questions, everyone!!
I've studied online gamers for over a decade using a variety of tools: online surveys, player interviews, psych experiments in a VR lab, and data-mining server-side data from WoW. I currently work for a game company where I continue my research in understanding gamers. My new book on the psychology of online games is "The Proteus Paradox".
Proof: see bottom of my homepage http://www.nickyee.com
Some highlights of past findings in online games and virtual worlds:
In WoW, 1 out of 2 female avatars is played by a man. 1 out of 100 male avatars is played by a woman. (http://www.nickyee.com/daedalus/archives/001369.php)
Contradicting the myth that online gamers are anti-social loners, 80% of MMO players regularly play the game with someone they know in RL, whether a spouse, family member, sibling, or friend. (http://www.nickyee.com/daedalus/archives/001468.php?page=5)
The avatar you use changes the way you behave. People given more attractive avatars walk closer to and share more personal information with virtual strangers. (http://nickyee.com/pubs/Yee%20&%20Bailenson%20-%20Proteus%20Effect%20(in%20press).pdf)
You can infer someone's personality from their WoW Armory stats. Players who are less conscientious in real life are more likely to fall to death from high places in WoW. (http://nickyee.com/pubs/Yee%20(CHI%202011)%20-%20Personality%20in%20WoW.pdf)
My New Book: "The Proteus Paradox" challenges the myths we have about online gamers and what actually happens in these virtual worlds. The book is available in print and ebook formats: http://www.amazon.com/The-Proteus-Paradox-Online-Virtual/dp/0300190999
One Caveat: I am not in any way representing the game company I work for, and as such, I'd rather steer clear of any questions about specific game titles made by them.