.Net 4 and Visual Studio 2010 are currently available in Beta 2, with a Go-Live licence. So now’s a great time to download them, play with the new features, and raise Connect issues about the bugs you find, right?
These products are done. Baked. Finished. It’s sad, but true, that generally by the time you start experimenting with a beta it’s already too late to get the bugs fixed. Raise all the Connect issues you want: your pet fix may make it into 2013 if you are lucky. Eric Lippert put it pretty well recently:
FYI, C# 4 is DONE. We are only making a few last-minute "user is electrocuted"-grade bug fixes, mostly based on your excellent feedback from the betas. (If you have bug reports from the beta, please keep sending them, but odds are good they won't get fixed for the initial release.)
Sadly, if you are playing with the betas, you are better off making mental notes of how to avoid what problems you do find, or praying any serious ones already got fixed / are getting fixed right now (eg: performance, help, blurry text, etc…)
 I’m exaggerating to make a point here, and please don’t think I have an inside track on this stuff, because I don’t.