Rock n Roll! This kind of news is exactly what I've been hungering for! I am extremely enamored with the idea of being able to push units of work (code+data) into the cloud for processing. These infrastructures have typically been Linux, Python/Java(script)/Perl based.
Being able to write code with familiar OS, tools and (hopefully!) .NET language of choice, and push that into the cloud makes me positively giddy!
I had presumed that the licensing costs of a Microsoft based stack would keep anyone but Microsoft from doing this. They still haven't released the cost of a Windows based EC2 so its still a question on the table.
The Amazon team will be at PDC. Be sure to check them out!