I am currently working on a project that will extend ArcMap (an ESRI product). The application includes a labeling tool with an embedded windows forms application all built in C#.
I will document my trials as this project evolves and post code that may be helpful to you C#ers. I was hoping to write 100% managed code for this project, but due to the COM interface only supported ArcGIS product suite all components are interoping to COM, which has been corky at times.
In all I have found the transition to C# from my VB, CF, Java past not too troublesome. This is my 4th .NET project and I enjoy working with it.