Rosscoe, he wasn't miscast, to me miscast suggests that the person was wrong for the role, and Jamie Foxx was completely right. He had just won an Oscar (as Trekkie said), he has a commanding presence, and can pull off Asshole really well--umm, he does it in every interview, red carpet event, etc so do it on film can't be much of a stretch.
Saying he was miscast is a bad excuse for the awful, misconceived, dull, boring, aloof, painful performance he gave in DREAMGIRLS. At first I didn't think much of Beyonce, but after seeing the movie a dozen times, I think she does a good job (though some of her line readings aren't all that great), yet she has the excuse that she isn't experienced in movies. As an Oscar-winner, Foxx owed us a first-rate performance, which he doesn't give.
I think Will Smith, whom I believe was considered for the role, would have been pitch-perfect.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"