One the one hand it is interesting, I guess mostly for mini-applications. On the other hand there is the risk that you can't take your app and run it elsewhere, you bind yourself to AppJet.
We don't want to get in the way of people hosting their own apps. We will at least release binaries for doing your own app serving and local development. You can already grab the source to the JS micro-framework. More details in our interview with Ajaxian: http://ajaxian.com/archives/appjet-develop-preview-deploy-al... - see the "Aren't you tied to the platform" question.
Yep, so, it looks like you can't get your app to run it youself even if you wanted to.