There's a nice message on the deadCENTER Film Festival blog to the filmmakers who submitted to them.
You didn’t drop your film into a vacuum – someone who loves independent film will be watching your movie. In fact, several people who love independent film will see your film. Every year, we have dozens of very enthusiastic, passionate and informed volunteers who want nothing more than to see the next Winter’s Bone before anyone else, and they’re convinced it’s hiding among the hundreds of films we receive for screening.
For filmmakers who find the "black hole" aspect of film festival submissions frustrating (and I don't know many who don't feel that way), this is a comforting message to receive. It doesn't change the fact that it's near-impossible to get useful feedback from a festival as to why one was rejected, but it's good to know that the screening committee at a particular festival is passionate about what they do.