My colleges have both Windows 7 and install Async CTP V3.
They have the right csc.exe file version but inside visual studio it does not recognize the async/await keywords.
When they try to compile the project is show the error message: Invalid token 'void' in class,
struct, or interface member declaration
If csc.exe has right version the installer upgraded .NET framework succesfully.
If VS2010 doesn't recognize the keywords, then either (1) the installer failed to update VS correctly, or (2) they have some third-party plugin like Resharper which doesn't recognize the keywords.
To check whether the installer updated VS correctly, please check the version of msvbide.exe from the instructions on this page
If the installer didn't update VS correctly, I wrote some other hints here: