This started happening to me last night. Dies after every couple of songs. I emailed support this morning at pandora-support@pandora.com and they blamed my phone like expected from tier one support.
If everyone emails them, maybe they'll get a clue.
I'm glad I just checked here. Yesterday I was going crazy. I tried my iPhone 4, my wifes iPhone 4, our old iPhones, and they all would turn off after 3-5 songs.