I'm currently listening to every CD I have accumulated, digitizing the ones I actually like, and discarding the ones that I don't like/probably won't listen to again/etc.
It's an interesting exercise. So far I've dumped ~30% of what I have listened to outright and am reserving judgment on some of the others. That's the top of the pile, so I imagine the discard rate is going to accelerate as I get into albums I haven't listened to for even longer.
For instance, I have all of the Against Me! full releases, but only listen to one of them, ever. The others I listened to when they came out and never again.
I guess people make a distinction between hoarding and collecting. You can have hundreds of gigabytes of movies and music and it's not hoarding; thousands of cds or dvds and it's not hoarding; an expansive library and it's not hoarding. I've started thinking of all of it as hoarding, though.