Hi there,
I just installed the contribution, and it almost works as expected.
If the selected person has something in his cart, the cart-image is shown to the left of all clients.
I've checked the mysql-database, and I can easily match a sesskey from SESSIONS with the session_id FROM whos_online, but apparently the same match isn't made in whos_online.php.
I have tried to put a product in my cart, and then go check in the module. Sometimes the right content shows up - other times, another shoppers content shows up (while my sesskey is supplied) - and again, sometimes no content is displayed - It seems pretty random.
I have no problems with cart content on the user-side of my shop!