Why do I hear.....

[choppedliver]

I definitely know that Kalimdor and the Eastern Kingdoms are on seperate servers.  In addition, instances seem to be on seperate servers of their own, since it was common in the beta to be playing just fine in instances while the outside world was crashing.

Although this thread has moved away from this topic a little, I thought some people would be interested in more information based on things that Blizzard said early in the testing.

Kalimdor and Eastern Kingdoms at the time were each on two servers (four servers total). Instances had their own server pair. Chat was on a fifth server. Thus a WoW "server" actually was at least five boxes total. It wasn't clear whether there was a separate, centralized database server, or whether the database was running on these machines.