IMHO, it doesn't seem correct to ask people for their "favorite bands". It would seem more accurate to ask them "when you're in a given mood, what bands will you most enjoy hearing?". At the right times, I'd be equally happy to hear Symphony X or Johnny Cash. But at any given time, I'm going to prefer one or the other. So why not just let the contributors spell out those similarity sets for you?
It seems to me that you're grouping things that are similar in some stronger sense than that they're the favorites of some people. And conversely, the way you're getting the data -- asking for favorites you'd be missing out on a bunch of minor bands that aren't anyone's favorite, but still enjoyed by people.
