I just needed to do something different while avoiding eating lunch at my desk. I had downloaded FlightGear this morning, after mentioning it to Gord, Julian and Patrick. Fired it up, and although it's a bit quirky, the price is right. I eventually figured out how to take off. The default plane is a Cessna, and the default field is just south of San Francisco (I didn't know that before I took off, but recognized the landmarks pretty quickly).
One of the cooler things about this flight sim is that it's open source - running on Windows, Linux, or MacOSX. It also downloads scenery as you fly, and is extensible by adding other locations and planes.