The CLR team has a survey for .Net 4.0 Beta 1 covering different aspects of performance, hosting, security, and application compatibility. If you’ve built new applications using beta 1 or you’ve tried recompiling or running older applications using beta 1 then you might have some useful feedback about the CLR.
I’ve been relatively happy with the beta CLR except when it comes to performance. Computationally intensive tasks appear to take quite a bit longer in this release, particularly on 64-bit machines. We tend to see this pattern in every release when working on WCF, and it takes a while to work thorugh the issues one-by-one.