Double threats?

Noodling around on a column I may or may not write, and I could use some brainstorming help. So two related questions:

1. What are some of the best -- and worst -- performances in film or TV by someone whose day job is as a musician/singer/rapper?
2. Do you think it's fair to say that rappers tend to segue better into acting than musicians from other genres? If so, why?

I have my own thoughts on this but I want to bring in some outside ideas before I decide whether this is worth writing.