Carry on....sorry I had to discuss the elephant in the room - but it wasn't addressed fully on his personal site or on the landing page for the book...soo.... :)
Also note that Sam Altman was a part-time partner before he sold Loopt. And I know plenty of YC co's who do have fairly involved side projects. The good thing is that the book's content often overlaps with being a founder. It's not like I released a "1001 Ways to Fold a Paper Crane" book.