I just noticed another small bug with WPBook. When I added gravatar support I forgot to add strtolower. The problem, if the user has capital letters in their gravatar it won't show and the default will be shown instead.
Easy fix though, in wpbook/theme/comments.php change line 38 from:
$grav_url = "http://www.gravatar.com/avatar/" . md5(get_comment_author_email()) . "?d=" . $gravatar_default . "&s=60&r=".$gravatar_rating;
to
$grav_url = "http://www.gravatar.com/avatar/" .
md5(strtolower(get_comment_author_email())) . "?d=" . $gravatar_default . "&s=60&r=".$gravatar_rating;
At some point we should clean this up and movie it to a function but for now this should fix the problem of capital letters in e-mails affecting gravatars.