Microsoft have released today 4 new whitepapers for Microsoft Virtual Server.  They all are about ~20 pages in length:

Hosting Core Infrastructure Workloads‘ has [from my point of view] perhaps the most value; there is updated information on identifying virtualization candidates and best practise for virtual server hosts. 

If you get inspired to build a host cluster, check out John Howards blogcast demo of it in action, and also his 5 part blogcast series on how to build the environment.