Last year (well, really early this year), Scott created a version of Conway's game of life in Silverlight.  Now he's created a physics simulation of a swinging rope using an algorithm he picked up from Gamasutra.  Note that this sample is written using the Silverlight v1.0 beta, so all of these calculations are performed using the browser's script engine and the perf is definitely respectable. 

Click the image below to run the sample, you can use the check box to add a wind simulation.  More info and source are available from Scott's blog post.