There are many exciting improvements, including better support for other test frameworks, VB.NET, F#, assertion generation, Code Contracts, and Stubs. Many of the changes are thanks to your feedback on our MSDN Pex Forum.
Also, together with Tao Xie, we are going to give a Tutorial on Parameterized Unit Testing at the International Conference of Software Engineering (ICSE) conference next month on May 17th in Vancouver, Canada. Go and register as long as slots are available. This is a great introduction if you are interested in using Pex or other test input generation tools to test your code, but you were struggling with the new concepts such as Parameterized Unit Tests.