You can use Spy++ to look at the properties of open windows on your system. If the window class name starts with "afx:" then the application uses MFC. As far as I can recall I've never seen a Microsoft product built on either MFC or Visual Basic. They apparently don't like their own dog food.

They tried doing stuff in .Net for Vista but had to revert all that; perhaps they've now come back to using it for real, but I know the new settings panel is done in C/C++.