Even as Amazon announces that it’s now selling more ebooks than physical books, “usability specialist” Jakob Nielsen reports that it takes you longer to read an ebook than a paper one: about 6% longer on an iPad, almost 11% longer on a Kindle.

Now that’s ironic.

Nielsen set his subjects down in some nice comfy chairs with good lighting. They read a story in print, then on a PC, iPad, and Kindle. Although there was a difference in how long it took to read in different platforms, Nielsen says, there was no difference in reading comprehension.

This is not a very scientific approach—maybe it takes you longer to read something a 3rd time than a 1st because you’re bored?—and the sample size isn’t nearly large enough to be meaningful. I’d be curious to hear the thoughts of people who actually are using these devices.

As for the Amazon number, there are caveats there as well. Ebooks are cheaper, of course. And Amazon is pushing the Kindle incredibly hard; if it pushed paper that hard, it’d sell a lot of physical books. And finally, there’s the novelty effect; we all remember downloading lots of songs from iTunes when we got our first iPod.

What I’d really like to know is, What percentage of those electronic books actually get read by their buyers? Or do they download because it’s fun and easy, but never actually get around to reading them?