For everyone that’s using a USB stick as a main unsling (root) device:
Did you create the “magic” .ext3flash device in the root directory?
http://www.nslu2-linux.org/wiki/Unslung/Ext3flash
This causes unslung to cease swap, and to tie down on disk-wear-and-tear.
Also, if you have a HDD attached as source for MP3s, you can create a swap file rather easily on the HDD. But thats not even necessary for firefly, afaik.