When should I use a struct rather than a class in C#?

Question

When should you use struct and not class in C#? My conceptual model is that structs are used in times when the item is merely a collection of value types. A way to

Answer 1

I was just dealing with Windows Communication Foundation [WCF] Named Pipe and I did notice that it does make sense to use Structs in order to ensure that exchange of data is of value type instead of reference type.