there is a paper (and epub) book about epub, but it has (judged by its TOC) rather the focus on how to get along with errors produced by inDesign epub export and how to make things work on apple devices since apple gives a crap about the specs, rater than som kind of "epub for dummies" which would be helpful for people who aren't web design savvy (like me).
http://www.elizabethcastro.com/epub/