There's a lot of cool stuff coming in Silverlight 4. Here's a couple of interesting links to get you started:

• Silverlight 4 Beta Page
• Tim Heuer's summary of the release, which has lots of info on features, tool support, etc.

And of course, if you're brave enough to be running VS 2010 Beta2, you can download the Silverlight 4 Tools Update that gives you full VS 2010 / Cider support.