Hi Neal. This sounds neat. I was thinking that, by the time the manual hits the bookshelves, Geiser will probably have matured to the point of having documentation: if you and/or the editors think it'd be worth it, count on me to contribute (or help with) a short chapter on Geiser (i'll understand it if you think it's out of scope; after all, although Guile is its best supported Scheme, Geiser is not Guile-specific).
I'm not very familiar with Guile's documentation, or with its implementation. On top of that, English is not my mother tongue. Despite of that, if you think i can be of any help during the edition process, feel free to drop me a line--i think writing about Guile would be fun. Cheers, jao