Anyone using Google App Engine?

I’ve been reading up about Google App Engine, which sounds interesting. It sounds like yet another “cloud” computer although one of the advantages is that this one is free, or at least some of the services are free and it integrates with the rest of the Google services which could be rather nice.

Of course there are disadvantages as its tied into Google which some people think is evil and your code could end up only being able to run on there platform and not others.

Has anyone used it? What do you think of it? Anyone done anything more than a quick look at the introduction page?