The idea seems to be, basically, make a better social filtering application. I definitely think there's space for something really cool here, but no one's done

The idea seems to be, basically, make a better social filtering application. I definitely think there's space for something really cool here, but no one's done anything close to useful yet, short of Amazon. If I were you, I would try to, at least for the time being, try to pare the idea down into something much smaller and more manageable. Once you have that done as a proof of concept, if it's still too small you can expand to other areas. Along the way, you will've learned a lot about what you'll need to execute on the bigger idea. Why not start with the movie suggester you mentioned later on in the thread?