The download links for Silverlight 3 are live on Microsoft.com
Microsoft® Silverlight™ 3 SDK Beta 1
Microsoft® Silverlight™ 3 Tools Beta 1 for Visual Studio 2008 SP1
Neither the Mix site nor the Silverlight site have any SL3 details as of 9:10 CST 3/18/09. It looks like Microsoft may have put the links live before SL3 is officially announced.
I look forward to seeing the feature list for Silverlight 3.
EDIT: WordPress went nuts and put a bunch of weird formatting in which was occasionally showing up in Firefox. I went into the HTML and ripped out all of the junk.
