I’ve been working on PressBooks for a little over a year now, and we recently did a complete overhaul of the site’s main design as well as the webbook read view.
One of the main focuses of the redesign, primarily for the webbook, was readability. We wanted the blocks of copy to be as readable as possible. The fonts we’re using are a classic font stack with “Minion Pro” as primary font and “Times New Roman” as a fall back. The full stack is : “Minion Pro”,”Times New Roman”, Times, serif.
Another important feature was to have the webbook view display properly for tablet and mobile with some responsive design.
If you’re a writer looking to get your book out in digital format, I highly recommend you check out PressBooks.