Right to left is still not supported and is not scheduled officially. You can vote for this feature and track the development using our Public Issue-Tracking System at http://www.telerik.com/support/pits.aspx#/public/silverlight/3296.
Chances are that we would not be able to implement RTL for Q1 2011, but we will have it in mind with regard to our development plans for future releases.
the Telerik team
Registration for Q1 2011 What’s New Webinar Week is now open. Mark your calendar for the week starting March 21st and book your seat
for a walk through all the exciting stuff we ship with the new release!