In the Workflow Administration Console, if you go to \Workflows\Workflow Definitions\{Workflow}\View Version History, it will give you a list of all the versions of the workflow selected as well as the Last Updated date and time value. What it does not show you is the user that published each version. I looked at the Workflow database and the user is captured in the workflow_history table, so I would think it would be easy to add to the interface.