This is pretty nice. I'll be using this service, though I'm not sure how heavily.
I run Vista using VMWare Fusion on my MacBook Pro for the express purpose of testing my CPAN distros, 3 out of 4 of which are XS. This testing rig was instrumental in garnering so-far perfect CPAN Testers records for the latest releases of Lingua::Stem::Snowball and Sort::External.
One thing left out of this initiative is MSVC. Installing and setting up the free version of MSVC is still a pain. And if you want to guarantee that your code is compatible with MSVCRT.dll, you need MSVC 6, and that means doing something "very expensive or very illegal".
Seems like the "very illegal" option isn't going to fly on MS-provided virtual boxen. MS could fix the problem at the source and disentangle the crazy manifesting dll hell of recent MSVC releases, but in the meantime it's still going to be much much too complicated to fully support Microsoft as an open source author.