I've had a Facebook since 2005 and before that I was an avid myspace user. Anytime I wanted information on any band I listened to, I'd go straight for myspace, but now, in 2010, I just search on Facebook or Google and it pops right up.
Basically, the Pandora link to Facebook is just like the Twitter link to Facebook. The purpose? to make it simple for your "friends" to see what Pandora stations you're listening to and what bands you like the most. It makes your Pandora profile link with your Facebook profile- your friends list moves over, along with your profile picture- thus "linking" the two sites.
Personally, I think it's pretty cool, but at the same time, it's odd to think of Pandora as a social networking site.
Hopefully, you're not listening to anything too embarrassing...because from here on out, everyone's going to know.
-Samantha Corrie Schulman