Seems like there are some change for the KMS in Windows 2008 SP2. Most important, there used to be a requirement of 5 physical requests to be able to activate server and 25 physical requests for Vista clients. With physical requests, I mean the request should originate from a non-virtual installed OS.
Though this has changed for Windows 2008 SP2:
A KMS hosted on Windows Vista or Windows Server 2008 SP2 now counts virtual machines toward the activation threshold.
In other words, environments which mainly consists of VM's now have the ability to setup a KMS withouth having to use workarounds.