Virtual PC is simply great. No more desks cluttered with expensive (sometimes crappy inexpensive) PCs for the purpose of testing applications on multiple platforms. What if an application runs great in all test environments but not on a particular live server? The last thing you really want to do is to install debug build software on a critical live server, ideally what you need is a perfect copy of the live server in a VPC session. Microsoft has the answer, a migration tool to replicate a live server in a Virtual Server 2005 session.
http://www.microsoft.com/windowsserversystem/virtualserver/evaluation/vsmt.mspx
Note, this software is in beta.