Well, I also signed up for the beta test of the app inventor. It wasn't easy to setup everything but the documentation for windows users is pretty good.
And it's really easy to "write" applications on it. Like a puzzle. But I don't like it. It's maybe good for people who know coding but not in java. They can click a bit and build an application. But there are a lot of limitation of functionality and you don't have full control of the application you build.
For serious programming use the Android SDK for java and the traditional way.