If you’re the kind of early adopter who installs .NET 4 Beta 1 and also wants the latest and greatest operating system (Windows 7), please check out Scott Hanselman’s recent blog post http://www.hanselman.com/blog/VistaUsersUninstallVisualStudio2010Beta1BeforeUpgradingToWindows7.aspx
 
While .NET 4 Beta 1 works well on both Vista and Windows 7, you’ll run into trouble if you try to upgrade from Vista or Windows 7 RC to Windows 7 RTM without first uninstalling .NET 4 Beta 1.  Scott’s blog has the details.