Allow users to define calculated metrics that use segments. For example, if you wanted to create a report that showed the top product categories including total revenue, total orders, % of orders that were $50 and % of orders that were from VIP members you'd define two calculated metrics:
% Orders VIP: [Orders where Member Type=VIP] / Orders
% Orders $50+: [Orders where Revenue>=50] / Orders
You'd then create a report broken down by Product Categories reports and include the metrics Revenue, Orders, % Orders VIP and % Order $50+
While you can get this type of information by running multiple reports and manually comparing the results, it would be much easier and useful if the reports could be supported directly in Site Catalyst.