I read this book about 13-May-2013. This is the first time I've read this book. The book is copyright 2005. This note was last modified Thursday, 30-May-2013 11:07:00 PDT.
This note does not contain major spoilers for the book.
The clever idea is in the title—that people will associate with people in their timezones, and that those who don't will be even more weirdos than usual. Given Internet connectivity, having your social group physically away isn't too hard, but having it out of sync still is.
Having said that, I didn't find the rest of the book after the clever idea to have all that much to contribute.