Do I have your book?

I was peering through my bookshelf, and discovered that I have a copy of Kurt Vonnegut's _Welcome to the Monkey House_ on it. I haven't read it. Now, it's quite possible I picked the books up at a used bookstore (I do that a lot) or on the street (I do that a lot too), but I didn't see a price marking on it, so the likelihood is I borrowed it from some poor person and never returned it.

Who did I borrow it from?