Mirko Rossini has finally made his Redis backend public. It's called django-redis-engine and according to him it's still in pre-alpha stage. From a quick glance at the code it looks like you'll be able to define database indexes in order to support queries that go beyond Redis' (meager ;) native query capabilities (much like with django-dbindexer). This is awesome because you won't have to maintain indexes by hand. If you want to see a stable and fully featured Redis backend please help Mirko. Just clone the repository from github and start playing with the code. Enjoy!
P.S.: Sorry for the long period of silence. We're still not finished with our final diploma exams, but we're getting close. Soon we can restart blogging more frequently and take the results of the previous survey into account.