This is a very interesting topic, but is also a touchy subject, and a very, very difficult subject to discuss, let alone in a civil matter. Some can accept color blind casting 100%, some are so-so about it, and some don't like the idea. Some opinions will be viewed on as racist when they clearly weren't meant to be, and vice-versa in this thread. 
From a Black/Asian P.O.V., I'd say that I am so-so about it. For instance, I wouldn't like Batman/Bruce Wayne to be a black man, but I wouldn't mind Harvey Dent/Two-Face being black (Denzel Washington was just perfect casting to me). Instances like Kingpin being portrayed by Michael Clarke Duncan didn't bother me. How many people know who the Kingpin is, and how many people in Hollywood had the commanding/physical stature to portray Kingpin? That was my argument about that. Since I already forsee Samuel L. Jackson as Nick Fury being brought up, I'll try to answer that one, too. This is a different case. Because two Nick Fury's exist in 616 and Ultimate Marvel, combined with the facts that Ultimate Fury was based on Jackson, Ultimate Fury as a General would arguably work better as a cameo, Samuel L. Jackson was arguably an idea that the writers of Iron Man and Jon Favreau fancied/wanted to cash in on, and they wanted to add Jackson's likeness to add quality to the film justifies his casting as Nick Fury in Iron Man.
In terms of Hollywood (non-superhero) films, I find the idea of color blind casting very interesting. Will Smith in I Am Legend, for example, is very intriguing because Neville doesn't necessarily have to be a black man. They wanted to cast Will Smith, and they did, not only because he is a good actor and a huge box office draw, but because he is able to do the job, regardless of race. Color blind casting is also convenient because in most Hollywood scripts, race is irrelevant. They cast whoever they want because they want to, whether it's based on acting skills, pre-conceptual ideas, to be "diverse," you name it.