With regular books, can you:
1. Carry around all of Wikipedia?
2. Carry volumes of research and technical information?
3. Conduct keyword searches on indexed information to help you find exactly what you're looking for?
4. Carry all of your textbooks (for students) or your entire library?
Once people learn that e-books could offer them these capabilities and conveniences, and some of the issues are worked out like open/standardized cross platform formats, optimal devices with excellent paper-like readability (e-paper) and great battery life, and content providers offer a simple and affordable delivery system, in my opinion e-books will really take off. I said e-books are "on the verge of going mainstream" because some of these things are starting to happen or are in the late stages of development.