Good thread idea.
I wanted to be able to carry many books with me at one time. I also end up reading a lot of thick books and my Sony is so much easier to hold, there's really no comparison. I also wanted the free public domain books.
Having an ebook reader has saved me so much money. I get ebooks and pbooks from the library, I get public domain books, and because of those two things I haven't paid for a book in over a year. (Could have been longer but I wasn't totally assimilated yet.)