Ok, honestly, I’m posting this so I can find it when I need it but Visual Studio 2010 uses a new report viewer that is compatible with .net 4.0.

http://www.microsoft.com/downloads/details.aspx?familyid=A941C6B2-64DD-4D03-9CA7-4017A0D164FD&displaylang=en

Bill McCarthy has some complaints (and a work around): http://msmvps.com/blogs/bill/archive/2010/04/19/upgrading-report-applications-to-4-0.aspx