1. cheaper 2 to 4 times (accounting for shipping), much more if you account international shipping or hardcover

2. conserve space, paper / trees

3. no bookshelves to buy and no more dusting!-)

4. lighter to transport, take more than a couple of them on a trip

5. download available immediately upon payment (or shortly thereafter), no more waiting a week or more (international) to arrive in the mail, or pay exuberant Overnight or Second Day Delivery charges

6. no shipping charges

7. never out-of-print

8. can be read at work without your boss noticing what you are doing;-)

9. reader software offers features like enlarging the font, highlighting, annotation, bookmarking and word search, also a look-up of words in installed dictionary for several languages

10. text-to-speech add-on

also read this independent study