You will soon be able to run Windows on Amazon’s Elastic Compute Cloud (EC2), in a fully supported manner. Jeff Barr says this is scheduled for public release by the end of 2008:

The 32 and 64 bit versions of Windows Server will be available and will be able to use all existing EC2 features such as Elastic IP Addresses, Availability Zones, and the Elastic Block Store. You’ll be able to call any of the other Amazon Web Services from your application. You will, for example, be able to use the Amazon Simple Queue Service to glue cross-platform applications together.

This opens up EC2 to a substantial new group of potential customers. They will be asking, of course, if the cloud can be made reliable.

Now, how about integrating with Hyper-V and/or VMware so you could easily move your servers in and out of the cloud?