I haven't done anything in .Net, touched the CLR since trying to assist VB.NET students in college, or even stayed at a Holiday Inn Express recently.
However, it's my understanding that WinForms is fairly analogous to MFC in that they're both supposed to serve as language bindings for Win32 controls like HBUTTON, HWND, etc. They're close enough that Visual Studio's context-sensitive help searches tend to bring up a keyword as it applies to WinForms, rather than as it applies to MFC.
You might find it worthwhile to try implementing in C#+WinForms various simple things that would be a piece of cake for you in C++/MFC. Sadly, I can't recommend Rosetta Code on this one as we've always had a dearth of GUI tasks, and our C# coverage isn't that great, either.