I installed the great theme Amazing Grace this morning.
Of course all the tweaking went fine, then came a problem. Every other gravatar was showing up in comments. The first one was a bit of the picture, then the second comment was fine, etc.
After an hour of hunting through the forums, I realized that each comment alternated a background. On the darker background, the gravatar wouldn't show.
I found the below code in the comment.php and removed it. That fixed the gravatar size problem.
<li class="<?php echo $oddcomment; ?>" id="comment-<?php comment_ID() ?>">
But - if anyone has a way to put the alternating background back in, and the gravatars work right, that would be cool!