Activity Monitor is the host page for the accelerometer plug-in and the example game/utility, link here.
VERY IMPORTANT: fun though this is, bear in mind it's a trivial bit of example code and meant for programmers. So don't spread it too widely or make grand claims for it. Hopefully some enterprising developers out there will see the code and leap into life to add accelerometer support to their apps.
Wonder if the plug-in will work from Python?
And why on earth haven't Nokia made more of the sensor, given how responsive it is??