I think it would cost quite a lot to get that set up for everyone, although it would be a great addition
To bad their website is throwing errors. Makes me wonder about the backend technology stability.
Personally I’m just set up with VirtualBox from Sun. Free for what you need, and I can run Ubuntu and XP alongside Vista. That gets me Safari/Win, Opera/Win, IE6 ,7,8/Win, Firefox 2/Win, Firefox 3/Win, Firefox 2/Linux, Firefox 3/Linux, and Opera/Linux.
For Safari/OS X I just use Browershots, although so far WebKit is rendering the same on Win as it does on OS X . So I may phase that out soon.
I have been using LitmusApp to test most of my stuff but may soon give up my subscription there. It is a great service but I recently set up Win XP on another laptop of mine so am able to test IE6 , IE7, FF2 , FF3, Safari PC, Opera and now Chrome.
Seems I am only paying Litmus for Safari Mac testing which can be done for free at http://www.browsrcamp.com/
If you have Win XP with IE7 installed then you can always grab Multiple IE to get standalone versions of IE6 and even IE5 .5 (and less).