Saw it about a year ago, really enjoyed it. What I thought was really powerful about the movie wasn't the fact it was about racism (there are plenty of movies about that), but the way it dealt with it, and the fact that it does it in an entirely realistic manner.
The movie doesn't condemn racists, with the plot focusing on innocent people who are victims of the evil racists. Instead, every single character in the movie (except for the teacher) is a racist, and every single character is a victim of the same shared hatred. And the solution isn't about killing/humiliating the evil, oppressive racists. Instead, the solution is about letting go of the hatred and anger and hopelessness that drives the characters to do horrible things.
Ultimately it's a very politically uncorrect movie, because it shows racists as being human beings, and because it doesn't blame a group of people for the problems in our society, but blames humanity and society itself for it's problems. That being said, screw PC, it's an amazing movie.