We've been running AdWhirl in production on AppEngine for over a month now. But, the code base isn't really ready for non-developer usage. Some important features are missing (house ads and stats). Added am important feature for us of parameters to custom events though, as that was a requirement for a campaign we started here and why we went into production when it wasn't quite ready.
The future of the code is pretty uncertain. It's all checked in to my branch on google code, although a dependent library for the UI has not been, as it's internal-only for now. We were planning on polishing it up, open-sourcing the UI library, and releasing something that people could just drop on AppEngine and go, but the new pricing changes have us all in a tizzy. Once the dust clears on that, we will decide if we can devote more resources to the AppEngine port.
-Casey