One thing that seems curiously missing from the Internet — based on my searching, at any rate — is how to encode to MP3 in Ubuntu Dapper. By default you can encode to FLAC and Ogg, which is a problem for me because the iPod doesn’t support either of these.
MP3 encoding is provided by the GStreamer lame plugin in gstreamer-plugins-ugly. However, the version of this included in the main/restricted/universe (I’m not sure which) doesn’t include the lame plugin; meaning that even after installing the ugly plugins, you cannot encode MP3s. This confused me until today when I discovered that the standard version doesn’t include lame.
To install the lame plugin, you need to enable the multiverse repository, then install gstreamer0.10-plugins-ugly-multiverse from the newly added repository.
Finally, you need to create a profile in GStreamer to specify the settings for encoding to MP3s using lame. Information about this can be found on the CD ripping page of the Ubuntu wiki. I changed the bitrate to 256kbps rather than the 128kbps recommended on the wiki page, but otherwise followed the instructions to the letter.
Hopefully this may be of help to other people with a similar problem!