I usually pick a fresh VM for installing an RTM build, but if you have loads of stuff on your (physical) machine, upgrading RC to RTM can be a real time saver.
Stack Overflow has a nice question Upgrading Visual Studio 2010 RC to RTM answered by Danny Thorpe (yes, two links: blog / wikipedia).
The order is really imporant, so lets repeat that here:
- Uninstall all the VS 2010 parts
- Uninstall the .NET Framework Multitarget package.
- Reboot
- Uninstall the .NET Framework client package
- Reboot
–jeroen
