I've got an old version of Creative Playcenter on my PC which allows me to edit the Gracenotes database (CDDB). Whenever I convert a cassette or vinyl to CD, or create a new CD for a client I've recorded, I always update the database. I also do it if I find have a CD that isn't already in the database - which happens quite frequently with 'budget label' CDs we receive for airplay.

So it's reasonable to assume that others are doing it, too...