I currently have just over 2100 songs on mine, most of which are encoded at 320kbps, but it's not even half full yet.
I currently have 9,000 songs, most encoded with --alt-preset standard
I've got 7 GB left on my 60 GB player.

If you pick an average of 10 songs per disc,
My collection consists of 478 CD's for a total of 6,469 tracks.
Do the math and you get 13.53 tracks per disc.