Page Brooks created a neat Silverlight application that controls his treadmill. Page openly admits it is a proof of concept and really lacks a real purpose, but from using some tools, he was able to create a very usable UI with minimal effort.
Here is a video of it in action.
Update: I put down the wrong person, Page Brooks created this. Sorry!
Update 2: Page has a 2nd part of this 3 part series on their blog.