I haven’t looked up survey results to confirm this, but I doubt that very many technical writers are producing their documentation in ebook format. However, some of the things that you need to think about when producing ebooks also apply to the new responsive HTML formats that current tools like Flare, RoboHelp, or WebWorks ePublisher can produce.
DBW has a good article that examines some of the design issues in producing ebooks that were originally based on a print design. Writers producing responsive help need to consider some of the issues raised in this article, even if they’re not specifically producing EPUB/MOBI/iBook files.
One purpose of print design is helping readers find their way from chapter title to text to sidebar to footnote. Another is decoration: using typefaces, color, imagery and ornament to embellish. Sometimes navigation and decoration work together to provide extra meaning (for example, in a cookbook, blue recipe titles can indicate main courses; red titles, desserts).
But navigation, decoration and meaning work differently in reflowable ebooks. Users change font and font size at will, causing reflow; decoration may or may not display well in different reading modes (particularly night mode); and light-blue heads may not be very visible in e-ink devices, and text to speech doesn’t mention that it’s reading a blue recipe title instead of a red one.
Developing reflowable and fixed-layout ebooks is a combination of design and technology. Developers need to know how to build solid, semantic HTML documents, and how to wield CSS to create attractive, useful books.