Google app engine is a cloud based platform by Google to enable developer to create and distribute their own applications. Currently it supports Java which was included recently and python ( 2.5 not 3.0) programming language. Also applications use GQL not SQL.
Any developer can start building apps and distribute them to their clients. And its free upto a limit:
1. 500 mb of apps
2.6.5 CPU-hours
3. I gb bandwidth for outgoing and incoming.
Paid plans are also available.
Documentation is top notch there. In fact much better than their Android apps center.

Also t the largest event of Google based on it is going to happen at San Francisco 19th May 2010.
Only trouble is how many APIs a programmer gonna learn for clouds? Google's , Amazon's and others? Of course a project for common standard have started but it is far away.