[Jellby]

I believe German uses spaced-out letters because traditionally it was written with blackletter type, and it's tricky to use italic or bold face with that. The Wikipedia article for "emphasis" confirms my belief. I have, however seen spaced-out text with roman type too, in a Swedish book, for instance.

Now that I think of it, it's probably a good idea to add spaces before and after the spaced-out text, at least if there are no punctuation signs there, as in this German example.

The Distributed Proofreaders wiki gives this advice:

em.gesperrt {
   font-style: normal;
   font-weight: normal;
   letter-spacing: .2em;
   padding-left: .2em;
}

(exact letter spacing to taste). The padding is so gesperrt words won't be off-center. Further complications arise when a paragraph starts with a gesperrt word, or in the rare browsers that handle letter-spacing differently, but this will work in most situations.

Still, your problem is the ePUB spec not supporting letter-spacing.