John Suler's Psychology of Cyberspace project contains a number of interesting articles about metaworlds from a psychological perspective. John is doing a study on the Palace as part of the project. He's spent a lot of time on the Palace, and reports his findings here. Good stuff!
 
A number of interesting articles about metaworlds can be found at Electric Communities, home of honorary Palace wizard, Randy Farmer. These guys were the creators of Habitat, one of the orginal graphical metaworlds and still an interesting case study in its present incarnation as Worlds Away, on Compuserve.

Signum, the online 'zine has published 4 great articles on the Palace. These articles concentrate on the interesting social and psychological forces at work in the Palace, including topics such as avatar usage, Palace addiction and social castes.
 
A great overview of the Palace in another great online 'zine, Urban Desires.
 
A great list of other palace-related articles and websites can be found here at the Palace website.