A couple of recent commentaries, excerpted below, suggest that the best sort of books for eBooks are ones that are intended to be read linearly, navigating through pages consecutively (i.e. most notably fiction). Both observers say that books whose usability is increased by flipping back and forth from one section to another do not make good eBooks.
Writing about the Kindle, Jakob Nielsen notes the problem with non-linear content:
The usability problem with non-linear content is crucial because it indicates a deeper issue: Kindle’s user experience is dominated by the book metaphor. The idea that you’d want to start on a section’s first page makes sense for a book because most are based on linear exposition. Unfortunately, this is untrue for many other content collections, including newspapers, magazines, and even some non-fiction books such as travel guides, encyclopedias, and cookbooks … The design decisions that make Kindle good for reading novels (and linear non-fiction) make it a bad device for reading non-linear content.
Later in the review, Nielsen broadens his comments to eBooks more generally. In addition to the issue of linearity, he also mentions that books that depend on pictures are problematic:
11 years ago, I wrote that electronic books were a bad idea. Has Kindle 2 changed my mind?– Yes — I now think there’s some benefit to having an information appliance that’s specialized for reading fiction and linear non-fiction books that don’t depend on illustrations and don’t require readers to refer back and forth between sections.
Paul Biba, in comments on using a cookbook on the Kindle, says:
The concept doesn’t work. This is not the Kindle’s fault, but the fact that some things are just not meant for an ebook format. When using a cookbook one likes to flip through it browsing for recipes. You look at one, go back and compare it to another … see if you can’t combine the ingredients of [recipes] … You simply can’t do this flipping back and forth with an ebook … Going back and forth from the table of contents to the index is a time-consuming process. The ergonomics of the whole thing is just not set up for cooking and recipe browsing.
This is really the first time I have come across a complete failure of the ebook medium. I can’t see how it is possible to make any change in the hardware that would alleviate the problem. There is simply no substitute for flipping pages and marking them with bookmarks … The ebook format is, by its nature, linear and this linearity is not adaptable to serious cooking.