Claudio had the smart idea to leverage the SharePoint grouping feature, to collect the data needed for the chart. One advantage of this solution is that the script is generic and can be applied as is to any list.
One limitation is that the solution relies on Google charts, which means that your data is going to travel over the Internet. This is fine for public information, but not suitable for secure data.
So I adapted Claudio’s script to make it work locally, using a charting tool. Here is a first demo:
I have partnered with FusionCharts, and in the months to come you’ll see more demos and tutorials that showcase their products. The charts come in two flavors, the complete v3 version and the free v2 version.