I can't find any standard for georeferencing of MP3 audio files. Nor, for georeferencing WAV audio files. Nor for georeferencing Ogg audio files. Nor georeferencing audio files of any format. Thus, I suggest here that anybody wanting to georeference MP3 files should stuff the latitude and longitude (WGS84 datum) into the Album field of the ID3 tag in the form LL@44.734,-74.339. That's two capital L's, an at-sign, the latitude, a comma, and the longitude. No spaces. You get 30 characters, so there's plenty of room for enough precision.
1 June: I couldn't get lame to work without segfaulting (on FC4). Other people have had similar problems. Since xmms will play ogg files just as well, and oggenc was happy to encode my audio files, now I have georeferenced ogg files. Here is a sample ogg file.
Send email if you want a copy of the Python program I wrote. It reads in all my GPS tracks, and takes the audio file's last-modified time to find the location. Then it prints the appropriate shell command to encode the file in Ogg format with the Album set as above.