1: Total quantity of books I own. Given that suzanne and I share a collection, I can't answer this for me personally. Together, we own somewhere between two and three.
Tons, that is.
At least, that's what I estimated when we recently moved -- 120 file boxes, weighing an average of 40 pounds each, plus the books in my office that I didn't move. The count is somewhere on the order of 3000 books, I think, most of which suzanne has cataloged.
2: The last book I bought. I'm thinking that the last time I bought books was at the bargain room of the Palo Alto Booksale, which is a sure recipe for something strange. If that's the case, then, the last book I bought would be this circa-1984 IBM Personal Computer Basic manual (olive-brown three-ring binding in a gray slipcover), which is a very near duplicate of the book I learned to program from.
3: The last book I read. "Read" is a very fuzzy word around the edges, particularly with nonfiction reference books that one's usually looking for answers in rather than reading cover to cover. The last one that I did anything close to reading through, though, is the ConTeXt-EN English-language ConTeXt manual, by Hans Hagen. I printed out the 300-odd-page pdf file and had it bound into a book a couple of years ago, and then a few months later a much-updated version came out.
4: Four books that mean a lot to me.
4.1. Viscous Fluid Flow: Second Edition, Frank White. This is one of the collection of engineering books that I inherited from my father, and one that has a few of his notes in it. It's also one that I use regularly in my own work, for looking up various equations and things, and has been for quite a while. The combination means that it's come to symbolize, for me, the less tangible engineering stuff I got from him.
4.2. LaTeX: A Document Preparation System, Leslie Lamport. TeX rocks my little desktop-publishing world. It's one of the things that introduced me both to open-source and to the joy of well-crafted software tools, as well as being an indispensable tool when I'm writing papers; it also later was my path into participating in open-source communities. This book is the one that I started with. (And it's autographed.)
4.3. Cyteen, C. J. Cherryh. This is one of the books that lilairen recommended to me, shortly after we met, with the comment that she'd make a lot more sense after I read it. (It's true, too; it's got a lot of useful words in, which particularly then she was using rather a bit to explain how she thought.) Thus, it's the book I think of when I think of our early book-sharing.
4.4. Towards a Symbolic Architecture, Charles Jencks. One of the things that fascinated me about the Myst games was how everything was symbolic; all of the details were chosen to work with the larger shapes and meanings of things, and the design became a language for indicating connections. Ever since then, I've wanted to work that idea into real-world things. This book, which I came across much more recently, is about very much the same ideas, but in real buildings, and it's in many ways a how-to book as well as just illustrations of what's possible.
4.5. King's Peace, Jo Walton (papersky). One of the things about hanging out on a newsgroup for writers is that one gets to watch one's friends going through the process from unpublished hopeful to published author. I still particularly remember her wondrous description of "It's a real book! With pages and everything!" when she first got to see a printed copy, and this book always reminds me of that, and of the joy of a dream fulfilled. And, besides, I rather like the story a lot, too.
5. Tag five people to pass the meme to. As with others, I'll just pass this along to whoever wants to continue it.