1) Total number of books owned?
854, not counting periodicals, catalogs, or manuals
2) The last book I bought?
Omnibus edition of the Journal of the Association of Engineering Societies, volumes XIII and XIV (1894 and 1895)
3) The last book I read?
I think the last non-reference I actually completed reading was Mark Kurlansky's Salt.
4) Five books that mean a lot to me:
I hunted Arnold Roth's Crazy Book Of Science for years and read it a thousand times when I was younger, so it must mean something. The other four I'll have to think about.