I never throw away books but when we went OS I had to put them all into storage. When we moved into this place DH got all our stuff from storage and left most of my book boxes behind. It's so wonderful having so many empty bookshelves because now I have an excuse to fill them all up again hehehe.
Storage is the perfect solution - one can hoard and de-clutter simultaneously.
I periodically cull crappy books from my shelves. I see no reason to use precious shelf space on something I never want to read again and wouldn't recommend to anyone.