I implemented a graphical drill-down on relational data with similar functionality to pivot tables. You could bring up an aggregate view on a table, like calls per day, then right-click on a bar in the bar-graph and choose an AND of a relationship. As an example, let's say it's "representative." Right-click choose "representative" and all of a sudden, you're looking at a graph of calls per day per rep.
The cool thing about that program, was that it was based on an OR framework, so all we had to do was to map it to a particular schema, and it could work with anything. It was implemented in Smalltalk running in a web plugin. It would be easy to do as a webapp in any dynamic language with a good OR framework and chart graphing framework.
The problem is that Excel already has pivot tables for relational data, and charting. The charting isn't interactive, so that would be cool. But you're not going to get people out of Excel just for that one feature. Because there are 50 other features in Excel that they use daily.
All the queries were dynamically built just by using the Object Relational metadata. The only setup needed was to map the schema, which there was a GUI tool for. (Not graphical, just GUI.) Do you think something like that could sell?
The cool thing about that program, was that it was based on an OR framework, so all we had to do was to map it to a particular schema, and it could work with anything. It was implemented in Smalltalk running in a web plugin. It would be easy to do as a webapp in any dynamic language with a good OR framework and chart graphing framework.