Having the ability to touch any word on the screen and have definitions, translations, and wikipedia entries pop up as you read (which is great for many of the older books) is a fantastic benefit over and beyond the simple fact that so many of the world's classics are available free of charge wherever you have internet access is a bonus that can't be overlooked. Honestly, in terms of studying books such as Gibbon's Fall of the Roman Empire, I find myself eternally grateful for such capabilities.
Not to mention, if you can read the book on your cell phone, you always have the right reading material on the toilet. :)