For those who may be interested, Jay Lee did a pretty good right-up on Relational Database Guidelines for MMOGs in September. I haven't checked to see if he's written any more works on MMOG theory. Heres the link:
http://www.gamasutra.com/resource_guide/20030916/lee_pfv.htm
http://www.gamasutra.com/resource_guide/20030916/lee_pfv.htm