The modular Django apps, of which Admin is the most prominent, are tightly connected to the Django ORM, and usually need joins. Even the session manager is database backed.
Joins in Appengine work almost like Django orm, `object.foreignkey`. But of course session, auth, admin, the things which make django such a joy are missing.
PDB not working on the dev_webserver, no dbshell, well they are almost showstoppers for me. I might use this to learn, ant to keep up to date if situation changes, but not for everyday use.