I might have done that (delay finishing a book) when I was carrying paper books around, so as to make sure I'd have something to read at another time - though I don't remember doing it, I might have done it.
But now that I have my e-reader, and always have some extra books in it, I don't think I'll ever do it. It might happen that I start a book and then start another one before finishing the first, but that also happened with paper books - usually, I'd just give up on the first. Now that the first one is still in there at all times, it's easier to get back to it
