first, let me say i think this plugin is very good, and i appreciate the effort to create and maintain it.
However i was having an issue with the avatars not showing in the sidebar, so i had a look at the code and compared it to the comments function in the default theme twentyten.
on lines 240 and 242, you had
$gravatar = get_avatar($comment->comment_author_email, $gravatar_size....)
but the section "->comment_author_email" is not necessary; using just get_avatar($comment, $gravatar_size) is sufficient to pull in the user's avatar.
This is also the method used in the twentyten theme functions.php file.
I just wanted to note this so that you could update your code if desired (which would also allow me to install any updates you make in the future ;) )