I am excited that Google App Engine has released multi-tenant support via namespace API. This should make it possible to white-label an appengine app (we have had several requests for this with modpoll) while avoiding forking, or spinning up a separate instance of the app. While there are disputes about what multi-tenancy actually should means from a feature perspective, if we can segregate db, cache and task queue as claimed that sounds like pretty useful start to me.