The Silverlight 4 RTW is here and available at http://www.silverlight.net. Make sure to grab the Silverlight 4 Tools for Visual Studio 2010, The Silverlight 4 Toolkit and Expression Blend 4 RC while youre there to experience the entire development experience. The RTM version of Blend will be released in the upcoming months, but for now the RC works quite well and is pretty stable. More to come as it is available. Just got all the bits installed and am ready to play.