We have different business units and set each one up as a "company" and associate users with their "company". The managers in each business unit are given "company access" in their customer profile, vs. "standard access". When the managers are in the customer portal, there is a drop down in the upper right corner that allows them to see all the people (in their company) or specific people's tickets, last ones with updates, open or closed and to search tickets that were submitted by customers in their "company". It takes a little maintenance to make sure new customers are added to the company, other than that...we love the feature. And they can make comments too.
