As a bookstore manager, I second the "it's better with two" opinion. When an author sits there alone, people are often nervous about approaching, afraid they'll find out the book "isn't for them" and then feel really awkward putting it back. I tend to position a staff member to walk up and chat a bit with the author when there's no one doing so already, so that people can come and take a peek without being centre stage.

On the rare and awesome two-author signings I've had, the duet always manages to entertain and chat with each other as well as those who approach, and it ends up making for a much better experience all around.