Another idea for things to post. Post images related to your book's theme so people can comment on them. In my case I can post images of Sutton - its natural beauty. So I can intersperse those in so people see what Sutton is all about. Again that's something where you have all the images ready to go beforehand in a folder, make a list of them, and then just cut-and-paste the URLs in one by one slowly during the course of the event.
People love photos!
