From what I know of C# (I believe I am right), value types are allocated on the stack and reference types are alllocated on the heap. But if a field in a class is value type, it is allocated on the heap rather than on the stack (I'm still right, right?).
With that said, I also know that every C# program is a class and is made up of classes. That should imply that any variable declared in a C# program, value type or reference type, should be allocated on the heap.
What I can infer, then, is that the stack may not be really used in a C# program. I say 'may' because there could be extraordinary cases, not that I know one, though.
You are mostly correct :)
Variables that are local to a method, however, are indeed allocated from the stack. This is the whole truth for value types. For reference types, the actual object, string, array, and so on, is allocated on the heap, but the pointer itself is allocated on stack.