Some feedback on the beta: The RadCartesianChart doesn't seem to handle null values or double.NaN correctly. In the 2011.3.1020.1040 beta it seems to draw a line up to a point in the top-left corner (see screen shot). Instead we need something like the EmptyPointBehavior of a RadChart series (extending it to support NaN as well as nulls), whereby we can specify whether we want a gap, a zero, or simply ignore the point.
These null and NaN values happen a lot when plotting industrial data versus time. For example, nulls occur due to instrument failure. And double.NaN occurs when a string is returned (e.g. "shutdown" or "calibration error") in the data stream, instead of a numeric value. If you can put yourself in the position of an engineer wanting to perform an analysis of an instrument failure or unexpected shutdown, these are some of the most important values of all, and must be handled well.