While I don't have many copies of the books all together, over the years I have probably bought two or three (okay, so maybe four or five) complete sets. I usually get the individual books at library book sales. I read mine so much that they wear out pretty quickly and I have to get rid of them. But once they are gone, I just reach into the back of my bookshelf and pull out a "new" one to fill in.
I like doing it this way, because then I don't have to worry about wearing the books out and spending a lot of money replacing them. Oh, and I don't feel bad about underlining my favorite passages in the older paperbacks. (Of course, it does take rather a long time to transfer the markings into the "new" books.
)
I do have one VERY nice boxed set, but I only really need to read HHB from it. No one ever seems to have HHB at their library book sale.
My sister has a one-volume copy with colour Pauline Baynes pictures. I usually use hers when I'm designing a costume.
But it is my firm belief that you can never have too many copies of CoN!
Tiffany