In this post David Anson talks about the improvements to the Data Visualization assembly in the April '10 release of the Silverlight Toolkit.
The primary goal for Data Visualization in this release of the Toolkit was to implement support for stacked series. I started out by looking at ways of adding that functionality to the existing series hierarchy (based on the DataPointSeries base class). There were two options that seemed interesting, so I played around with each for a bit. But while both definitely seemed viable, neither felt completely right to me.