Virtual PC (And VmWare) can certainly be a lifesaver. Daniel Petri's Website has a bunch of Virtualization topics that can be an interesting
read. Just look under Knowledge Base!
As some have eluded to, Virtual PCs can also be great for testing software. Heck, you could have a Windows 2000, Windows XP, Windows 2003, Windows Vista-compatible app and spend days trying it out by rebuilding boxes or finding boxes with the right OS. Now you can just have nice clean images ready to go!
Jon.