We have been using Gravatar to pull in author photos with posts:
<?php echo get_avatar( get_the_coauthor_meta( 'user_email' ), apply_filters( 'twentyten_author_bio_avatar_size', 46 ) ); ?>
Most of our posts were created by me, but I changed the authors to other users.
We used to have Gravatar and coauthors plus working together nicely, but today all the Gravatars started displaying as me rather than the coauthors.
I tried & did not have success with: get_avatar( get_the_coauthor_meta( 'user_email' )