Probably as a testiment to the fact that I no longer watch Saturday Night Live, I just read about this controversy today. It seems SNL used Fred Armisen, an actor of Asian and Hispaic decent, to depict presidential candidate Barack Obama in a debate skit.
Armisen has played Prince in a skit as well, with no controversey response. To me it is a bit reminicent of the old blackface comedy skits, but in "post-racial" America maybe people aren't up in a fury about actors playing characters of another race for comedic purposes.
For me the larger issue has more to do with SNL's casting generally. Perhaps they didn't have a black actor that resembeld Obama closely enough. It might be equally problematic to have one black actor who was a stand-in for every black male they choose to satarize. In my experience, SNL's cast is overwhelmingly white. The subtext could be interpreted as only white people are funny. (Obviously not true, if you've ever seen Dave Chappelle.) But why is it so hard to find black actors for Saturday Night Live's cast? If they did have a more diverse cast, it would probably change the dynamic, the humor, and the audience of the show. And that might not be a bad thing.