Much has been the expectation about Silverlight 5 ever since the fire-starter in December 2010
Silverlight 5 has been the expectation of every SL developer ever since the SL4 release and the huge momentum surrounding HTML5 on the web. While HTML5 is definitely promising, Silverlight and other proprietary plugins have their own strengths in terms of rich capabilities such as Digital Rights Management which have evolved to a great extent.
In MIX 2011, Scott Guthrie unveiled Silverlight 5 Beta among much fanfare! You can read about the complete list of Silverlight 5 Beta features
In the meantime, Silverlight 5 RC is available for download from here