Santa Monica
Santa Monica downtown, Monday afternoon. Everyone is 17-25 and on their way from the beach, on their way to a party. Don't people work here? More Starbucks-per-square-inch than in Manhattan, and that's saying alot. Movie theaters and pizza parlors, city-provided free WiFi and street musicians everywhere.
So far, LA is living up to it's party-town atmosphere, at least near the ocean.