With IS 2010 the icon from the EXE that I registered a file extension to would automatically be assigned to files with the extension. In other words if I registered .wxc files to MyApp.exe then all .wxc files showed up with the current icon for MyApp.exe. Now that doesn't happen in IS2011. I'm sure there is a way to do this - but cannot figure it out. By the way - when IS2011 upgraded my installs from 2010 it left out my shortcuts and file extensions entirely!
you need to assign a unique ProgID to your file extension(s) (You can use the same progID for multiple extensions if they will all have the same behavior)
A ProgIDs Node will appear in the middle panel (you may have to leave Components and come back to see it). Your new progID will appear under ProgIDs. Click on the progID and set the Icon Property to whatever you want.
By the way - I could not find anything about this in the help files... At least from the direction I was looking (from File Associations) - perhaps there's something under ProgIDs - but that would be an odd direction to find it from IMHO.
