I stopped presenting acquaintances with copies of my books after the first one. I only continue to contributors, while I now favor exchanges with colleagues.
After the first gifts, I came to the conclusion people have little esteem for a free book given away by its author (unless he/she is a very famous one). Suddenly they feel superior to the author. They seem to have more consideration for a book they've bought because their money is involved. By the same token, I think even a stolen book has more value in their eyes, because their crime involves some risk. In other words, the a priori value of a book for its average owner is simply its price.