Organising books at home (cont?)

I'm like a cat lady, but with books. Also, not a lady. Ask MetaFilter One of my first postings on Petrona, if not the first posting, was about the number of books in my attic, house, cupboards, and the number of book titles noted on Amazon.co.uk, in notebooks and so on. Well, here is a posting on a site called Ask Metafilter, from someone asking how to organise their personal library. (I found this via my rss feed to Superpatron.) There are lots of useful-looking answers which I'll try to get around to reading sometime. (And maybe even trying to implement if any of the suggestions seem manageable and don't require a PhD in librarianship or computer science or both.) Mind you, Superpatron says "I have more books than bookcases at this point so I have some perfectly good books in storage, which often makes it easier to retrieve them by borrowing them from the library when I need to read them rather than sifting through poorly cataloged boxes." Seems a reasonable point of view -- but my problem (and my need for a file system) is that I don't remember which books I have stored and which I've given away to charity shops or the library. And no, the obvious punchline has not yet happened to me (borrowing a book from the library and finding that it used to be mine).