According to the delightfully nerdy MusicMachiner.com, Seattle is the 13th most musical city in the US. Here's how they got that statistic:
I gathered up the top 50,000 or so U.S. artists, found their city of origin and tallied the number of artists per city. From this tally I calculated the number of artists per 1,000 inhabitants in each city. The more artists per 1000 inhabitants, the more musical the city.
Neat idea with some unexpected results. Beverly Hills is #1, San Francisco is #2, and Nashville is #3, but New Orleans, which I assumed would be in the top 10 at least, is all the way down at #36. And New York City is #37! I suppose if it were just kept to Brooklyn it'd be a much different story. If you throw a rock in Brooklyn, you hit a musician. (But it's not nice to throw rocks, so don't do that.)