I have used this workflow many times with customers if there is a problematic installation. I would always backup the Registry keys if you plan to delete them!
The main Autodesk installation files/registry keys are located in 3 places the registry:
This is the sample key (folder) you would delete for Revit 2011 x64:
The Autodesk hotfix/updates installation files/registry keys are located in the registry here:
Thanks to Almas Suljevic for this great tip.