Bryan Larrick critiques the new Kindle app for iPad in Improved Reading Experience? No. I particularly like his points on how design impacts readability:

It’s hard to overstate the importance of healthy margins and whitespace in good design. [“¦] The words are the most important aspect of a book. That’s intuitive. But, presentation is very important. Having ample margins helps the eye flow over the text and makes it easier to move from one line to the next while reading. Making the margins smaller in the app hinders the ease with which the eye can move over the page, making the book harder to read, not easier. Also, it’s just ugly.

So obvious, yet so often ignored on web sites and in apps.