Simply seeing a candidate with an e-book reader wouldn't necessarily sway my vote, although it would certainly indicate a demonstrated appreciation for technology. Seeing them read an e-book on a laptop or PDA would work for me in the same way.
However, if the candidate showed that they do read e-books (whatever they read them on), and recounted their advantages in terms of practicality, portability, materials conservation, ease of use, etc, I would be impressed. That would indicate a better understanding of the real value of e-books, as well as an understanding of the digital world and how it is improving the rest of the world.
Based on the chart I linked to, I'd guess Barack Obama has a better understanding and appreciation of those issues than the other candidates' responses suggest. Being younger than the other candidates, and a family man, I'd think he has a strong understanding of computers and the digital world. If I expected to see any of them reading an e-book, or at least having a good knowledge of what they are, it would be him.
But have I seen any overt demonstration of a knowledge of technology above the others? No.