So I took a look at the books I currently own, and discovered they broke down into 58% fiction, 42% nonfiction. But that didn't make for a very satisfying pie chart, so I delved deeper into each category and came up with these lovely images:
Fabulous fun! Look at that -- a solid 50% of the fiction in my home is "juvenile" -- mostly what they call "middle-grade" nowadays, in the 9-11 age bracket or thereabouts. These are clearly books to cherish and to re-read. Mystery novels come in at 22%, "general" fiction (you know, Austen and Dickens and the like) are 18%, and fantasy is 10%.
Here we have my nonfiction books -- and the influence of birding on my bookshelves is such that a good 20% of that 50% nature/birds category is for the birds. In the "history" category I lumped biographies and autobiographies, along with most of the adventure travel books. But it's mostly just plain history and comprises 26% of my collection. Art is 11%, and miscellaneous, at 13%, is a hodgepodge of a few books here and there on myth/folklore, psychology, religion, hard sciences, and sports.
So there you have it -- fun with pie. Don't you wish you had a database of your books to play with?