Is there any reason for Amazon EC2 to not support Vista/XP/7 images in the cloud? I know that EC2 is primarily a platform for deployment of applications, but I can't imagine that costs or difficulties would be that much higher to also include some client-side platforms. After all, these are just virtual machines, and all it takes is a basic install to make such platforms available (ok, and maybe license negotiations with Microsoft).
I work for a startup called http://LabSlice.com and people have shown interest in using the technology to share VMs of test apps with their customers. Every so often we get asked for a Win7 image, and I assume that if we get asked then surely this would've been something asked directly off Amazon to support...
See the related question Windows desktop (XP, Vista or Win7) EC2 AMI for QA testing