“In some ways, the e-book is yesterday’s mass market,” says an executive at St. Martins in an article in the New York Times. Although I think he means "today's mass market." But it somehow makes sense in the context of the article, which looks at one more facet of the changing book business. It's hard not to feel that everything has changed, and that "yesterday" is about as fast as it's changed.
I have signed lucrative contracts for paperback rights to books that originally had only the hard cover rights sold. Although the royalty on the ebook, at least according to this article, is better than it is on a paperback.