I wait until I can't find anything, then go mad and really enjoy clearing it all up, which is what I am doing in my potting-shed lean-to at the moment.
The music room was the last one to get the 'treatment'. I got DBH to build me a ceiling to floor bookshelf with shelves deep enough to take filing boxes. I bought 30 filing boxes and now all the music is filed by instrument, then composer, then owner of that piece of music. That was last summer. As a result, I know now what I always suspected - that DBH is the main culprit, NOT me or DS. It was worth all the hard work for that alone. So now, if he leaves his stuff in piles to fall off the piano and stool, we simply pick them all up and stuff them into one of his boxes, but can still find our own!