If you believe the scientific data on the subject, black men (at least in America) have, on average, incrimentaly larger erect penises than white men--nothing to write home about, or even feel if you're on the recieving end. There is a somewhat more pronounced size differential, on average, for the flacid state, although it's not exactly night and day in this case either.
What does bother me is the unfortunate pressure this discrepency between the myth and the reality places on normal black males. Everyone assumes that you're hung like a horse, when in reality you're probably hung like most everyone else.
Once when in college, a black friend of mine (I'm white) wound up with two co-eds back in my apartment. These girls really were quite wild and they wanted to have an orgy--well at least as close to one with just four people. I dropped my pants first and the girls were ecstatic, as I sport a fairly thick 8 incher. Then my friend took off his pants, exposing a somewhat smallish, maybe 5 inches and not very thick, black dick. The girls were so quiet, you could hear a pin drop. I really felt for the guy. To make matters worse, both the girls more or less focussed on me that night and he got the leftovers. I'll never forget that, and how bad I felt for him. Ever since that night, I've been aware of the other side of the black stud myth. For that reason alone, I wish we could bury it along with all the other racial stereotypes which we seem to continue to perpetuate.
My two cents worth.