I had to change the Song.find_or_create_from_pandora_song method to get the song URL from pandora_song.audio_urls['HTTP_128_MP3'] rather than using audio_url, which doesn't seem to contain any data.

I also had to add HTTP_128_MP3 to station.rb DEFAULT_AUDIO_FORMATS so that it would be included in songs from the station. HTTP_192_MP3 is no longer provided to non-Pandora One partners (even if the user login is Pandora One) and the only partner credentials that seem to work are Android.