This seems like an important idea:
But what if you like bands that you don't have on iTunes?
The bands that show are independent of what you have on iTunes -- it shows *everything* that iLike knows about. I believe includes shows that Ticketmaster has, shows that artists enter, and shows that users report. So it'll show a lot of things, and if it doesn't have the bands you're looking for, someone can add them easily.
Whoops, I just realized this is referring to the iLike Sidebar. *I* was talking about the new iLike "Local Concerts" app for the iPhone.... whoops ;( Still, a very cool app.