I gave my Exploring C# DSLs: LINQ, Fluent Interfaces and Expression Trees talk today at Miracle Open World 2012 about C# Domain Specific Languages.
The slides are now available here.
… and the demo source is available as a git repository on bitbucket here.
Note that some of the source is just mocked implementation, the goal was not really to show production level quality – but rather concepts. The quality of the few tests and commit messages reflect this.