That problem (requiring an MP3 encoder) is fixed in upstream rhythmbox
svn: http://svn.gnome.org/viewcvs/rhythmbox?view=rev&revision=4980
** Changed in: rhythmbox (Ubuntu)
Status: Needs Info => Fix Committed
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0.9.8 iPod writing not working in Feisty
https://launchpad.net/bugs/86920