Here on slashdot you can read:

New research suggests that the clear screens and easily read fonts of e-readers makes your brain “lazy.” According to Neuroscience blogger Jonah Lehrer, using electronic books like the Kindle and Sony Reader makes you less likely to remember what you have read because the devices are so easy on the eyes. From the article: “Rather than making things clearer, e-readers and computers prevent us from absorbing information because their crisp screens and fonts tell our subconscious that the words they convey are not important, it is claimed. In contrast, handwriting and fonts that are more challenging to read signal to the brain that the content of the message is important and worth remembering, experts say.”

Personally I think this is nonsense. The people commenting on this article (hit the link for those) agree.