I've... probably halved? over the years. Now I'm getting down to reference works and antiques, and it's getting a bit irreducible. I've just picked a reference book off the shelf that I know had a fairly short print run in 2004 and was $49 then, and it's on Abe for between £228 and £690(!). I freely admit I don't touch many of these books from one year to the next, but the idea of them being put out of my reach in that way makes me nervous.