The rep system was really unnecessary, though getting rid of it now I don't feel it has really changed much with the forum, at least the parts I frequent.
When it was in effect I felt the fear of negative rep would keep more timid posters from daring to disagree with the fanboy herd. I never really cared, honestly, even though I'd get bombed with neg-rep every time I posted something "unpopular" on a subject or series that fans considered "holy" or whatever.
I'm sure if rep still existed, my recent posts in an Evangelion related thread would have netted me a metric ton's worth of negatives...