So the way this is going to work is that I'm going to use average percentile ranking to order the films. Then I'll work from bottom to top pitting the films against each other: Film 27 vs. Film 26, then the winner of that vs. Film 25, etc. To determine the winner of each pairing, I'll look at the ballots than ranked both films and see which film the majority had ranked higher. (There's a good chance that Film 1 will win ... but where's the mock-drama [and the post-whoring] in that?)
All this is another way of saying: If you only rank the films you like and don't bother to rank the films you don't like, you could be hurting your own cause.