There are some breaking changes between Beta2 and this RC, and we want to make sure that existing sites can update to the final release quickly once the final release is out. As such, you can only use the RC for development right now - you can't go live with the new APIs until the final release is shipped (which will be soon though).
You can download today's Silverlight Release Candidate and accompanying VS and Blend support for it here. Note that Expression Blend support for Silverlight 2 is now provided using Blend 2.0 SP1. You will need to install Blend 2.0 before applying the SP1 service pack that adds Silverlight 2 support. If you don't already have Blend 2.0 installed you can download a free trial of it here.
The final release of Silverlight is not that far off now. It has been a pretty amazing project that has come a long way in a pretty short amount of time.