I'm really liking App Engine for my projects, but there's one crucial element that it's missing that to me and is more important than anything else. There's no API for creating App Engine instances.
We use App Engine in a couple of ways. First: when we build client web sites, we lead the client through the setup and configuration and then add us a developer. It would be nicer if we could script all that and hand them the key when it's done.
Secondly, we use App Engine to host multiple instances of the same app. So for example if you want to run Arecibo, you have to create an App Engine instance, download the code, alter the configuration to match to App Engine instance, then do a push up to App Engine. I'd really like to have an automated approach to this: come to the Arecibo website, click a button and then you have your own instance running.
This latter use case is the most important to me as it allows me to write an app, then deploy it across the web multiple times easily. Just like can write any other app for phones or desktops, you can easily deploy web apps across the cloud. I'm still so impressed about how easy Arecibo is to deploy on App Engine it's nice having a well known target.
There currently exists the App Engine Marketplace, but as I gather this is a single app that's a multi tenant system, I don't want that.
Yesterday at OSCON I was able to get the ear of Sean Lynch from the App Engine team for a few minutes. It was a great chat and good to find that there are plans to resolve this. No promises on details or timelines, but good to hear its happening.