Ugh... I gave an entire lecture on this at GDC Austin in 2009. Wish I had the time to go into it but I'm currently catching my flight from a full 4 days of Indiecade straight to a full week of GDC Online (ex-Austin). Suffice to say there are plenty of places where MMO AI can be changed -- and some companies are in the process of doing so (not necessarily released yet). However, there is a sort of mystique about some things. One of the major comments about my proposals in 2009 was "but that will break Tank-Healer-DPS!" To which I replied, "so?"
That sounds incredibly interesting. Please return here once you've rested from your trip
 I think I found the slides from the talk Dave mentioned, for anyone also interested.