Why not allow users to see how their friends have rated movies? Right now you can vote on movies, your votes can be added to the average score, and you can make your votes public. But there is no way to see how a particular individual has rated a particular movie without a substantial amount of effort.
What I'm suggesting is that each movie's page has a hyperlink right below the average score titled "your friend's scores" that leads you to a separate page. There you find a list of how highly each of your friends have rated the movie out of 10. And for people with no friends, there would be a simple way to add people whose opinions you respect onto the list. If you enjoy somebody's written review, you could "subscribe" to their rankings and their opinions on movies will be added to your list. Of course, not everybody will have seen every movie, but this option could tell you which movies your friends have seen and whether or not they liked them.
Note that people are already ranking tons of movies and that these rankings are already public, so this shouldn't be all that hard to configure. Make it happen, imdb! This probably could also work as a facebook application, although it would have to start from the ground up.
By the way, I've been on a tear of watching movies this break, here are my most recent scores:
Eastern Promises - 10/10
The Shining - 9/10
1408 - 6/10
National Treasure Part II - 5/10
No Country for Old Men - 9/10
Merry Christmas guys.