in reply to Hording books and manuals.
Originally picked up as part of a project in which I planned to catalog web sites by DDC code, I may eventually find myself using it for the books about the house. Eventually I'd like to have fully classified, organized, and database-entry-ized every piece of media I own. (/me adds project to already lengthy "to do" list).
As to the question of what to do with old books? Depends. My gut instinct is "keep them". In boxes if necessary. Too many times I've moved or simply desired to have less clutter and gotten rid of books, magazines, audio recordings, etc. Only to regret it. Many are simply not available at the present time or their replacement costs are now skyhigh). Unless space or other expense is at a critical level, pack old books in good plastic bins and stuff them in the rafters of the garage, the attic, a corner of the basement, is my opinion.
Or, as the best possible alternative, bundle them into reasonable groups and sell them on eBay. If your books have any market value at all, someone there will probably pick them up. Don't try to guess what they're worth, start the bidding at $0.01 and then make sure to add a reasonable S/H fee. This way your books get to people who actually want them, and it's likely that if there is any latent demand for your books, that the price will get bid to an appropriate level.