This guy has posted an interesting project based on the third version of the .NET Framework, which implements a ray tracer by using some of the new features of this framework, like LINQ and lambdas.
From LukeH's post: "... Although we often demo C#3.0 using databases and XML to show off LINQ - it turns out that the new language features really are also great for applications which have little to do with querying. Ray tracing, for example, is certainly not one of the prototypical scenario for query and transformation of data. Nonetheless, I found quite a few places in the code where C#3.0 and LINQ to Objects really improved the code - making it easier to express what the program was doing ...".
Not related to XNA, I admit, but nice screenshot, uh?![Again, imagine XNA, XAML, DX10 and .NET Framewor 3.5 ...]