We were having some performance issues on lower end PCs so we used the EnableRedrawRegions parameter to diagnose.
We found a clash between the standard Silverlight Toolkit BusyIndicator and DataGrid which was causing the page to rapidly and constantly redraw. We have created our own BusyIndicator and that fixed that issue.
We now have the same issue when opening the Telerik Silverlight ReportViewer (i think to do with the BusyIndicator that displays during report load). Even after closing the ReportViewer the issue persists for lifetime of application. Have you seen this issue elsewhere? - do you know of a resolution?