insert an ipod, select a bunch of songs, and drag them to the ipod. RB will start doing the copy/conversion process, but for every song, it's leaking a file descriptor.
This can be seen in /proc/(pidof rhythmbox)/fd/

After a while, the per-process limit is reached, and rb starts popping up hundreds of dialog windows, which causes metacity to freak out.
The only way out of this death spiral is to kill rb and metacity from the console, as X stops responding to events.

running rb in debug mode also shows the leak ..

 (17:21:08) [0x19f3770] [attach_output_pipeline] rb-encoder-gst.c:600: attempting to open output file file:///media/IPOD/iPod_Control/Music/F47/NIN%20-%20Good%20Soldier%20(sam%20~ZL.mp3
(17:21:08) [0x19f3770] [error_cb] rb-removable-media-manager.c:962: Error transferring track to file:///media/IPOD/iPod_Control/Music/F47/NIN%20-%20Good%20Soldier%20(sam%20~ZL.mp3: Error opening file '/media/IPOD/iPod_Control/Music/F47/NIN - Good Soldier (sam ~ZL.mp3': Too many open files

rhythmbox-0.12.3-1.fc11.x86_64