I've got an iRiver music player, too. 40G internal hard drive. I got it because it 1) played ogg format which was rare at the time and 2) works like a regular USB hard drive without needing proprietary software to load files on it.

It doesn't get as much use as it used too. Now it is simply the backup storage for all the ripped music, since a number of other devices I carry around also conveniently play ogg. (Entourage Edge, GP2X Wiz, Zaurus SL-C860).