Thanks to TidBITS, which comments:
Do you read faster or slower on a device like an iPad or Kindle, in comparison with a physical book? The overall answer, according to usability expert Jakob Nielsen, is about 5% to 10% slower (with the same comprehension of what was read). That's statistically significant, though not all that much slower. (We suspect it may have to do with years of familiarity with the form factor of the book.) More interesting was that on a 1 to 7 scale, users rated their satisfaction at 5.8 for the iPad, 5.7 for the Kindle, and 5.6 for the physical book, with the traditional PC trailing behind at only 3.6.
Update: Ganesha Games says:
This is so odd to me. Since I have the kindle, and then the iPad, my reading speed has increased by roughly 25%, with better comprehension (I read in English, which is a second language to me, so the in-built dictionaries and word search functions are a bliss).
The extreme portability of both devices also means I can read a lot when on trains, at the dentist's, in line at the post office or bank, and so on, and the availability of cheap or free reading materials have vastly increased the quantity of my reading.
But I've always been a heavy reader so maybe I'm out of the norm (a novel a week, plus a non-fiction book spread over maybe three weeks if it's heavy, plus rulebooks for games and reference materials/blogs/websites on a daily basis, and 7-8 comics a week are an average for me).
When I was a kid and teen, my father drove us to the library every Monday when it was open in the evening. And I remember that every week I would borrow and fully read about five to six books. Per week! Plus school reading. Of course, each book was not War And Peace, but still, now it seems rather extraordinary. 'Smatteroffact it must have been extraordinary, because I hardly remember seeing anybody but me and my father there in those evening hours.
I am probably also faster reading on the iPad, I haven't tried to measure it, but at least I now prefer it over reading on paper.