Well, I've collected anime cards, books, cds... but not so much as to put anyone out of business. And I stop collecting one thing when I am collecting another thing. So I don't get to accumulate so much that everthing can't be organized.

Now it's music books and sheets. Aside from piano, I got 1 violin book and 5 guitar. Basic stuff. Plus loads of pop music that I don't know; I didn't buy those, they were given to me.
How do you sort your sheet music? By era, genre, composer? Title or opus numbers? By difficulty?
PS. I want to put every pdf e bay seller out of business
Yes, please! Why sell scores when they're supposed to be public domain? And why sell for unreasonable prices?
But if you really want to put every pdf seller on ebay out of business, don't limit yourself to piano. Or classical for that matter.