I've done a lot of customization of Artoo with Rockbox. There are a few bits here and there that I have to work a bit on, but the results have been well worthwhile. I even got a new tagging program, Tag & Rename, to replace my beloved Ultratagger, which I have been using for many years now, but unfortunately only works with mp3 id3 tags. Tag & Rename, on the other hand, handles many codecs, including Ogg Vorbis, which I've been experimenting of late. The rename and field substitution, copying and transfer capabilities are much improved over Ultratagger (which, as I must point out, served me faithfully for about six years).
While there is no way around the fact that MPEG-1 Audio Layer 3 is a compromise between file size and quality, the use of variable bit rate kept the former in check while providing the best the latter could offer for the format. Vorbis, however, is variable bit rate by nature, and is capable of much higher quality at comparable bit rates as mp3s. I played around with the different settings last night. The results were interesting; at standard mid-bit rate level, Vorbis has a much fuller sound yet yielded a much smaller file size.
I adjusted the settings until the resulting file size was in the same ballpark as the mp3s and they sounded great. Raising the mean bit rate even more would result in better sounding files, of course... but the file size gets much, much larger by that point. In some cases, the resulting file was double that of an mp3 of the same track (given that they are both VBR, I the file sizes are more related to one another than they are to the length of music).* As it stands, the differences between the two formats become more subtle at the higher bitrates.
I have replaced most of the copies of my mixes in Artoo with Ogg Vorbis files. They are an improvement in clarity over the analogous mp3 files, even though the file sizes are roughly the same. While I do indeed have audiophile tendencies, the files were so large that they almost defeated the purpose of compressing them in the first place. In a way, that's annoying. With the mp3s, I knew that I was getting the best possible results I could out of the codec. With Vorbis, the codec is capable of even better sound than these. The aural advantages of encoding the files at a higher mean bit rate are not enough to warrant the space they would take up in Artoo, but it still bothers me that there is something slightly superior that I'm not using. Not even that's just "out there," like HD-DVD or Blu-Ray (didn't anybody tell them that they mispelled "Blue?"), it is something available to me right now.
* Another advantage of the Ogg Vorbis codec is that unlike the mp3 format, it is naturally gapless. Mp3s can and will play gapless if they are encoded with the proper metadata to do so (LAME), but in Ogg Vorbis, it is the nature of the beast.