Web developer Joe Hewitt and team posted an alpha version of Tilt -- an rudimentary iPhone game that takes advantage of the iPhone position sensor.
The is simple, but does provide an example of how to detect the iPhone's position. Andrew Mager describes the game:
This was my favorite game presented at the hack-a-thon. Javascript afficianado Joe Hewitt, along with help from Nicole Lazzaro, Colin Toomey, Kent Bye, and Felipe Ortiz, built a game that claims to be 1.5 dimentional. Flip, who likes to eat falling leaves and butterflies, will only catch his dinner if you rotate your iPhone in time for him to be under the falling food. You can try it on your desktop or laptop browser, but good luck trying to rotate your screen.
Wired profiles Joe Hewitt, who has been one of the most visible iPhone web developers who has put out templates and other hacks to help with iPhone web development.