I used to be interested in this type of service, but then I got an SSD. With an SSD it takes about 5 seconds to boot windows through parallels, and now cross browser testing is no longer a chore. I am willing to admit that I pirate windows for the sole purpose of supporting IE with my webapps. It would be too expensive to do it legitimately, so my solution is not for everyone.
I think MS provides VM images of Windows for testing IE.
And when you finally have them set up, you know what prize you win? You get to debug some crazy-making IE issue. As far as I'm concerned, free isn't enough: they should come with masseuses and bottles of good scotch in compensation.