My first impression, without looking at it - "Threesome" is a really bad name for a book on polyamory, because it has so many purely sexual connotations for so many people. It even further blurs the line between polyamory and swinging (which many non-poly community folks already think are the same thing...).
If I saw this on bookshelves and were looking for a polyamory resource, I would look right by this one.
"Listen, or your tongue will make you deaf." - Native American Proverb