If so, why? Absent-mindedness? You love them that much? First Editions for the shelf, but paperbacks to read?
If not, why not? Not enough space? Not enough money? Too sensible to do something so foolish?
I don't have very many multiple copies, as far as single copies go. I do have some individual paperback versions that are also included in hardcover collections of individual authors, though not very many. We have a few first editions, but we treat them like our other books, and have been known to actually read them!
The only book that immediately comes to mind that I own two copies of "on purpose" so to speak, is The Cloister Walk, by Kathleen Norris. I bought the paperback, and read it at a time when it really helped me, even though I was reading it for pleasure, without thinking it would have such an effect. A couple of years later, The Tim bought me a hardcover copy that was remaindered. Every once in a while, I think I'll donate the paperback copy to the library book sale, but it seems too much like a friend to let go. So both copies exist on the shelf, side by side. I pick them up and read parts over again from time to time (it's that kind of book, you don't need to read it through all at one time).
(Sadly, I have only one copy of "The Fabulous Mr. Ed." But that makes it all the more special...)