There is a story on NPR today about ebooks — apparently Amazon has reported that they are now selling more ebooks than DTBs (dead tree books). For every 100 physical books they sell, they sell 105 ebooks, so the scales are just beginning to tip — but still, that's pretty significant, considering how many people I know still have major reservations about ebooks.
I think I'd consider myself exclusively an ebook reader now. I haven't read a DTB in a long time, and the last one I read was simply because that was the only format I could get it in (it was also a library book). To me, there's no contest anymore for the books I read: Ebooks don't take up any space in my house, I don't have to drive to the library or the bookstore to get them, don't have to wait for library books to come in or return them in time to avoid a fine. And it's far easier to hold the Nook and turn the pages than it is to hold a real book.
For the books I collect, of course, I still buy "real" books, but for reading copies you just can't beat the advantages of ebooks!