Sorry, True Grit, Black Swan, The Fighter, and The Kids Are Alright, but you won't be going home with any Best Original Score Oscars: the Academy has determined you all ineligible.
As for Carter Burwell's True Grit score and Clint Mansell's Black Swan score, the Academy has decided they're both "diluted by the use of tracked themes or other pre-existing music." More specifically, Burwell's music is largely adapted from 19th century hymns, while Mansell logically made use of Tchaikovsky's "Swan Lake," thus making them a little too un-original for being an original score.
The scores for The Fighter and The Kids Are Alright (by Michael Brook and repeat-offender Carter Burwell, respectively), meanwhile, were deemed "diminished in impact by the predominant use of songs." Which is another way of saying all the catchy, mainstream tunes on the soundtrack had Academy members bee-bopping too much to even notice the underlying score, I guess. I have yet to hear if Eat Pray Love will be similarly disqualified for playing that Florence and the Machine song in the TV ads so often it made me spit with rage.