Total number of books I've owned: 
That was a funny one. Next question. (If it's all-time, it's multiple thousands. If it's currently on hand at my house it
might be less than 1,000 because I've been doing some cleaning out.
Last book I bought: I am attempting (again, this time with the help of an online study group) to learn to read hieroglyphics. As a result, I just purchased
Concise Dictionary of Middle Egyptian by Raymond O. Faulkner and
The Tale of Peter Rabbit (Hieroglyphic Edition).
Last book I read: The Machine Crusade by Brian Herbert and Kevin Anderson.
Five books that mean a lot to me:
Wow, five. Hmm. Well "a lot" is easier to answer than "The most" or "more than any others."
Have Space Suit, Will Travel by Robert Heinlein. One of my all-time favorites as a kid, I still re-read it occasionally.
Hackers and Painters by Paul Graham. It explains so many important things much better than I ever could.
The Miles Vorkosigan novels by Lois McMaster Bujold. No deep meaning, just a whole lot of fun. (This is cheating perhaps because there are about a dozen books in the series.)
The Martian Chronicles by Ray Bradbury. I read this when I was about 10 in the aftermath of the TV miniseries that was based on it. I was quite disappointed at the lack of ray guns and space battles. ("They flew to Mars to visit Hicktown, USA? Hell, I live there already!") Rereading it a couple years later, I came around to a different understanding of the stories.
The Mind of Egypt by Jan Assmann. A fascinating (but difficult and dry) read about ancient Egypt.