New C# 3.0 feature - Partial methods
This feature is apparently available with the Beta 2 of VS 2008 (Orcas). I need not say much apart from stating my opinion that it looks like quite a useful, straightforward addition to a world of generated code living peacefully alongside your own code in a rich, interactive fashion.
You can read an excellent rundown of the feature, its capabilities and its limitations, over here: C# 3.0 partial methods - What, why and how?