Measuring g-forces with an accelerometer and an Arduino always makes for some interesting times, however it's what you can do with the data that truly reveals some interesting possibilities. One example of this is demonstrated by the people from the coolarduino website who show how to use an accelerometer as part of a gesture recognition system.
As the data can be captured from an accelerometer in numeric form, it's relatively simple to reproduce physical movements and compare them with previously captured data - and thus gesture recognition is possible.
For more on this interesting concept, check out the interesting coolarduino website. And for more, we're on twitter and Google+, so follow us for news and product updates as well. If you're looking to recreate such a project, a good start would be with the AM3X accelerometer module:
This tiny 3-axis accelerometer module can operate in either +/-1.5 g or +/-6 g ranges, giving your project the ability to tell which way is up. Ideal for robotics projects, tilt sensors, vehicle data loggers, and whatever else you can dream up. For more information and to order, click here.