The current implementation of commenting on Tableau Server is a little half baked. It would be great if this worked more like Facebook where you get notifications if someone comments on a workbook you posted, in a thread that you have participated in, or on a workbook / view you have marked as a favorite. Also, give the user the option to receive email notifications.
Something like this could go at the top of Tableau Server to tell users that there is activity on their workbooks:
Another possibility would be to add a news feed feature to server that would be a historical list of events that are important to the user. It could contain things like alerts for data source updates / failures, new workbooks / data sources getting published, first time users to server, alerts for server errors, daily server stats, comments on dashboards / views, snapshots of views you are subscribed to, etc. Administrators would see more things in their news feed and it would be configurable. You could also set the server to push certain events to you via email alerts.