I bought an ereader because I hadn't been able to read novels in more than 10 years due to eye damage. Large type books didn't help because it didn't address my specific vision problem (ghosting around letters). Now, I can adjust type size and font to get the right spacing and contrast to read comfortably.
Honestly, after only a DAY of use, I regret not having bought one the same year they came out. I've had my Kindle keyboard for 2 years now. The main disadvantage I see to using an ereader vs. buying a paperback is that it is harder to flip back pages to reread something (i.e. in a mystery). The second disadvantage is that you can't resell your 'used' ebook. On the plus side, it's way easier for me to share my library with family members, something that wasn't easy to do in the past. Also, cookng from an ereader - not so good.