The majority of the charts right now choke heavily on large datasets.

http://dojo.telerik.com/urIne - This example shows 20,000 points on a scatterLine chart.  It takes a very long time to render this and, when panning or zooming, the redraw time is huge.  This means it is completely unsuited for any large data sets (I've found anything over ~1000 points creates a major lag for the end user).