I use Firefox for browsing, falling back on IE only when I find a site that doesn't seem to work properly with FF. I happened to be using IE the other day when I visited Jim Crafton's CodeProject article on using DocBook on Windows, and I noticed something I'd never seen before: the ability to copy code examples from the article to the clipboard with a single mouse click:
The "Copy Code" option doesn't exist under FF, alas, but the idea of making it easy for readers to work with an electronic book in a natural fashion is a good one.
In fact, it's an example of a more general idea: presentation of a book's content should take advantage of the natural capabilities of the presentation medium. Another example is also shown in the image above: the ability to dynamically collapse and expand a code fragment. Such presentation capabilities don't affect the fundamental content of a book, but authors do need to keep them in mind, because authors can often do a better job of specifying the natural "copy to clipboard" or "collapse/expand" chunks. (At CodeProject, the chunks are presumably determined by the content in some HTML block.)
The fundamental idea is this: although the content of a book is essentially static, the presentation of that content need not be.