My mom got me a very cool present for Christmas. Thanks, Mom!
I already had a large number of mp3s, but now I am redoubling my efforts to organize and document them with appropriate mp3 tags. To that end I am using two or three things on my PC, from iTunes to Rio's own management software.
So far, iTunes has the coolest playlist options - I can basically write any criteria for a playlist and iTunes will get those songs. For instance, I have a playlist of songs rated four or five stars that I haven't listened to in two weeks. If I rate a new file with five stars it just magically shows up on that playlist. Of course, iTunes doesn't sync with my Rio Karma and I haven't found an option to export a playlist in m3u format, but I have done some shenanigans with iTunes's xml data, xsltproc, and perl to produce m3u files in bulk. I can drag those playlists to my Rio, and all the associated songs go with it.
There are some caveats, but this thing is quickly becoming my constant companion. I wish that it has iTunes-style playlists built in. I wish that I could rate songs and use that data to sort music. I wish that I could assign my own metadata. I wish that I could access all of the ID3v2 tags.
Anyway, whereever I go, I can finally hear those Tom Waits albums that I have lurking in my collection. That pretty much means that I can listen to my music all day at work. 20GB means that I don't have to listen to the same albums over and over again, so I will finally be giving Cake a rest.