A common music fan scenario: You’re going to a huge festival where lots of your favorite bands are playing all at once. You want to see which of your friends are going, and to what acts — and if there’s a hot new group, you want your friends to share some actual music with you beforehand. Traditionally, you’d have to do a bunch of calling or emailing around to figure out who’s going where. But concert producer C3 Presents — the folks who put on events with more than 100 acts, like Lollapalooza and Austin City Limits — have been busy taking advantage of social web services coming out over the last year, and to great effect. Especially, it says, through using Facebook Connect.

The company integrated Connect with Lolla and ACL a few weeks ago — Connect, launched last year, lets other web sites get user data from Facebook as well as send it back to Facebook for a users friends to see. In this case, both of the festivals’ sites are designed so that you first see a list of band names in the lineup. Mouse over any band and a window will pop up showing you how many people are going on Facebook, as well as the option to sign in using Connect. If you sign in, you’ll also see how many of your friends are going. Click on a band that one or more friends is going to see, and you’ll be taken to the band’s page, with a box beneath showing your friends.

Already those sites are seeing massive growth: A 99 percent increase in page views, a 34 percent increase in pageviews per visit and a 20 percent increase in the average user’s time on site compared to its pre-Facebook numbers, according to C3. What about other traffic drivers, like big lineup announcements? C3 says traffic had been holding steady this year versus last — including when lineups for both festivals were leaked prematurely — and only saw the surge when the integration went live.

But it’s not just about Facebook, of course. C3 also introduced ways to share concerts you’re going to back to other sites, including MySpace and Twitter. More than 70 percent of the traffic that it’s getting from these sites is through the sharing feature. Meanwhile, MySpace is still in the process of rolling out its own Connect-style service.