The funnest thing I ever got paid to do was a compete in a competition. I the "Unix Guy" was tasked with using C# and .NET to build a client/server database application. Our resident "Windows Guy" was given the same specification and tasked with building the same application on Linux with Trolltech QT toolkit. I had NO .NET experience and he had zero Linux experience... I had the app done in 2 days. At two weeks, the boss called the competition done even though my competition wasn't complete yet. This was all done so my boss could prove to the higher ups that .NET was the way to go.
What fun programming tasks have you been paid to complete?