Jakob Nielsen has been conducting reading comprehension tests among a variety of reading devices. He says people can read books fastest in printed book form. But, people seem to find the experiences fairly comparable:
[On a 1-7 scale, the] iPad, Kindle, and the printed book all scored fairly high at 5.8, 5.7, and 5.6, respectively. The PC, however, scored an abysmal 3.6.
I completely agree with the PC based book reading experience as it exists today. The Kindle for the Mac is surprisingly unusable compared to actual Kindles, Kindle for iPhones/iPod Touches, or Kindle for Android devices. Plus, it’s very difficult to read a book when there are so many other distractions on a computer.
Nielsen’s tests suggest that people can read faster on books in printed form. However, I think that result will vary tremendously based on how familiar people are with reading on an electronic device. Also, picking the most comfortable font size, font face, brightness, and contrast will make a huge difference. A person with poor vision will clearly have better luck reading on a device where they can blow up the text to something easier to read.
In my own case, I’m sure I can read more effectively on my Kindle for Android app than I can in book form. Why? Because I get around to doing 90% of my book reading either in the dark, or at times when I don’t have a printed book with me.