I've been wondering why Netflix doesn't come up with some kind of personas. Each member of the household can rate movies, and then it can make recommendations for an individual or combination of them.
Is there a way to compute a "taste distance" for a combination of users reliably? I think if you just throw their ratings together you'll get a point with impossible taste (except if they like the same movies, in which case it won't matter). Maybe return only movies that were in the recommendations of both users?