Here's a copy of a post I made in a zdent MaryJo article:
AppEngine seems to me years ahead
Google's approach and advice is simple: 1) don't use SQL, as it is not easily scalable. Use a NoSQL server from the start. 2) Write a web-page and Google will scale it. Simple. Smart. And did I mention CHEAP! You can run a medium traffic site for FREEEEEE.
So if you aleardy have an SQL site up and running, you might want to give Azure a look, otherwise by going Azure you'll just create something that you'll have to rewrite tomorrow (as a microsoft developer i bet you're used to that).
My prediction: Microsoft will copy AppEngine to the letter, replacing Java with dotnet. Microsoft developers, why wait? use AppEngine today