1. no clutter. I have an issue with clutter from hardcopy books I bought years ago.
2. instant gratification--can go from a purchase/lend to reading in seconds.
3. can carry thousands of books on one device--great for travel, convenience, and reading what I want when I want.
4. customizable display
5. easier to get promotional (free/very cheap) books and free public domain books.
6. keeps your place for you without dogearing.
7. searchability (this is minor compared to 1-6 though. Paging through ebooks is more difficult on a device if you don't know the string you're searching for)