All you profiler writers will want to try out your profiler on the latest and greatest!

Information on getting beta 2 of CLR V4 and Visual Studio 2010 is available here.

The beta 2 docs for the profiling API start here.

There have been some bug fixes between beta 1 & beta 2 that may improve life for your profiler.  It's also worth noting that, for those of you dabbling with getting your profiler to attach to a running process, the method to get an instance of the metahost API has been renamed (since beta 1) to CLRCreateInstance.  If you're looking for more information on how to make your profiler attachable, I will be posting an entry on that as soon as I can.