Now that Google allows Java on App Engine, I'm wondering what effect this has on a choice of web framework for App Engine.
Is there something I'm missing - do any frameworks work well on App Engine?
Actually web2py is very light and since ~1.50 on GAE, it caches all bytecode compiled models/views/controllers.
Nevertheless you need to consider that by default is has datastore based sessions and this may add some overhead when compared with framework that do not have sessions working on GAE (at least not by default).
The web2py DAL itself does not add a significant overhead when compared to the naive Google datastore APIs.