That's right, it's been a while. I'm nuts for Peanut, Walter and Achmed.
SILENCE! I KILL YOU!

It is indeed a "right place" "right time" kind of humor that is dependant on the correct delivery. There is a difference between bringing up noticable yet truthful/funny differences in ethnicity and cultural ways, and making fun of people for being different.

You must make sure that you aren't being descriptive in a hateful, or degrading kind of way. Although some comedians can get by by doing just that...it still isn't best to risk it. Most people have a sense of humor about themselves and their backgrounds; but in the same respect, there are a lot of people who don't.

As long as you keep it pretty clean and respectful, there usually isn't much of a problem.

The reason Dave Chapelle is so funny, is because he took sociological stereotyping, and blew it out of proportion, which is what everybody usually does anyway. He simply put into skits, what races tend to think about each other based on common stereotypes that he over exadurated a bit.