In the course of various projects I've been working on lately, I stumbled across two great blogs focused on MMO data mining that I'd never seen before:
PARC's PlayOn Blog - This site is mainly focused on WoW, but also looks at other games from time to time. Lots and lots of juicy data here, and they also have a few posts on character abandonment, which is interesting in the context of the black box series I'm working on now.
Armory Data Mining - This site is focused entirely on data gathered from character profiles on WoW's Armory. There are some very interesting analyses here of battleground compositions and class talent distributions.
Both of these sites are very interesting because they're run by researchers who aren't part of the dev team and therefore don't have special access to any data. If sites like this can exist based on only public data (as Armory Data Mining does) or data mining from in the game and surveys (as PlayOn does), imagine what a developer with free access to all information and some professional engineers could achieve.