Compare the reading speed of a paper book with the Apple iPad and Amazon Kindle 2, those electronic devices will slow you down by as much as 10.7 percent. That's according to a survey of 24 participants reading various Ernest Hemingway short stories.
Those participants took an average of 17 minutes and 20 seconds to read each story, but were found to read 6.2% slower than printed paper when using an iPad and a surprising 10.7% slower on the Kindle.
This is bogus. The survey reported that participants complained about the iPad's weight and the Kindle's weak contrast. I suspect they had never used either of these devices before participating in this survey.
I use both of those devices to read extensively, and sure, at first I was distracted by the novelty of reading a book on the iPad, and its weight was a bit heavy. That weight issue was quickly alleviated by using Apple's book-like case that helps support the somewhat heavy iPad.
And yes, the Kindle 2's contrast was a problem until I figured out how to perfectly adjust the lighting for it as I read.
For a valid study, Jakob Nielsen and his consultancy at Nielsen Norman Group need to find test subjects who've already been using an iPad for reading, and have grown accustomed to it. Same thing with the Kindle. Do that, and then compare that with reading in print, and I think the results would be quite different.