Despite the fact that my cats are antiliterary, I have collected a great many books, which I often lose track of. On digging through the quaint and curious volumes, I have sometimes discovered that I have two and even three of the same book. Oops. It's kind of forgivable when you consider that I cycle books through a lot. I have a 1350 sq. ft. townhome. There is only so much bookshelf space. I have sold off chunks of my collections at pennies on the dollar just because I couldn't keep them around anymore. In all the confusion, I forget which books I still have. Most of the books I've sold, I don't miss. Occasionally, however, I do and, without digging through the collection, I find and buy another copy (and sometimes another).
I heard about LibraryThing from Kevin Smyth, who has created an online catalog of his vast collection. I started cataloging mine some months back, but have only recently resumed the task. It's kind of addicting. I think it's seeing the number of books grow. Somehow, when viewed as an online list, it's more impressive than looking at the bookshelves.
But LibraryThing is more than an online catalog. It's a place to chat about books with other bibliophiles and to find people whose literary tastes match yours. For each book in your collection, you can see which other LibraryThingers have the same book. Sometimes you may find that your the only Thinger with a particular book; for example, I am the only one who includes H. W. Wilson's two-volume Ironclads in Action in my library. (I have a few other sole volumes as well.)
You can also view other people's reviews of books. You can rate each book in your collection and see how other people rate the same book. You can tag books in your collection so that you can quickly retrieve a list of every book you have on, say, medieval warfare (many) or Pictish symbols (a few).
LibraryThing is also a place to share resources such as scans of book covers. There are a lot of these supplied by places like Amazon.com, but a lot of more obscure titles or editions have no images available. With scanner at hand, I'm able to supply previously unavailable book cover scans in just a few minutes.
So now I'm plugging away at the library. At this posting, I have only 83 books recorded. That's a small fraction of the collection and I've got a lot of work ahead. I've added a widget for LibraryThing at the bottom of my blog. It shows a random selection of five books from my library, but also has links to my full library on LibraryThing. I'm pretty sure this won't solve my problem of buying multiple copies of a book, but I may at last have some clearer picture of what I've got on the shelves.