"I don't go into the hospital and let the janitor perform surgery on me, you know what I mean?"
Anthony Mackie (The Hurt Locker) on rappers-turned-actors. The blog entry from "BV on Movies" also brings up some old quotes from Samuel L. Jackson and Nia Long about rapper-actors.
Personally, I'm ambivalent about rapper-actors. Will Smith and Queen Latifah have turned out some exceptional performances, and Smith has earned two Oscar nominations, while Latifah has one (for Chicago). On the other hand, guys like Ice Cube, Ludacris, and 50 Cent are average actors, and that's being generous considering some of their performances. I like Ice Cube and Ludacris, but for the most part, they, like a lot of rapper-actors, are just taking roles that should go to trained African-American actors.
LL Cool J and Ice T have been good in parts tailored towards their personalities, but they're also deficient. I think that a guy like Mos Def doesn't get enough credit for how good he is as an actor.