I was memed by Johnny-Dee. So here it goes:
Number of Books I Own: I honestly cannot say. My shelves are two-deep and then some, but on the other hand, I don't actually have much shelf-space. On the other hand again, I own more books than are in my apartment, since I have boxes of books that I didn't bring to Canada. Before I went off to college, the number of books I owned was somewhere about a hundred, including old children's books and the like, but it has certainly undergone a massive expansion since then.
Last Book Bought: I think the last book I bought was Dorothy Sayers' The Documents in the Case, but I'm always losing track. It could also have been this one.
Five Books that Mean a Lot to Me:
In no particular order, and without committing to these being the books that mean the most to me:
1. Thomas Aquinas, Summa Theologiae.
2. G. K. Chesterton, The Man Who Was Thursday.
3. C. S. Lewis, The Lion, the Witch, and the Wardrobe.
4. Dorothy Sayers, The Mind of the Maker.
5. Joseph Butler, The Analogy of Religion, Natural and Revealed, to the Course of Nature.
I could also add Newman's An Essay in Aid of a Grammar of Assent, Julian of Norwich's Revelations of Divine Love, Euripides' The Bacchae, Sophocles' Oedipus at Colonnus, Shakespeare's Henry V, Austen's Pride and Prejudice, or Eliot's Romola.
Since I had such difficulty answering the questions myself, I won't tag anybody. Feel free to chime in with your own answers, though.