We use both. It's easier for me to load my iPad with books and take it to camp than it is to bring them all with me. Also, my daughter reads SO much that I can't keep up. We would have to go to the library every other day. Lol! Our library allows you to borrow ebooks, so we do that a lot.
I have our curriculum on an ebook and it makes it so nice. I have it in book format also.
I also would like to add ebooks have so many neat features. I love posting favorite quotes from the book I am reading onto facebook. I have received so many free ebooks. They are amazing. I think when you love books you just love them no matter what form they come in. They are also easier to read in exteme light. I still love the feel of actual books. I don't think ebooks will ever replace actual books but they are a nice addition.
I have free ebooks, but won't pay for any. When a book is no longer useful for me, I'd rather sell it, donate it, or give it to someone I know. You can't do that with ebooks. I tend to keep books for years, so I don't worry about getting rid of a book just to end up needing it later.
Oh, I don't have to worry about charging a real book either.