The last three versions of Firefox have supported the W3C device orientation spec. Before that, and going all the way back to Firefox 3.5 more than two years ago, Firefox supported a vendor prefixed version.
It's one of those things that are obvious in retrospect, but computers have had accelerometers used for sudden motion sensing for decades now, and most manufacturers employ this tech in some form or the other in their upper-end modules.
Yet it took one bright individual to figure out that there's no point in using the accelerometer just for SMS, when in fact, its API can be exposed to the world for whatever other accelerometer-related needs. I don't know why other manufacturers haven't followed suite, but given the state of the industry I would not be surprised if patents are, in one way or the other, to blame.
If you are building something for wide market use then definitively don't use these new features until they are supported by multiple vendors. But before standardization can happen things have to be tried out, I don't see what all the negativity is about when it comes to new features in chrome (I don't get the same vibe with Firefox only features).
It's better, in my opinion, to have a working prototype of a feature working and used by some early adopters than to build standards in a vacum.
Those early adopters need to know those features my disappear or the apis change and be ready to fix their code.
It seems to only react to two axes (beta and gamma -- in other words, if I rotate my MBP on a flat surface, nothing happens) -- is anyone on a device that provides alpha as well? I know the iPhone does, but this demo doesn't seem to work in Mobile Safari.
The hdaps Linux kernel driver for Thinkpads' sensors (don't know about the other flavors) can export the data as a joydev, which can be mapped arbitrarily - I've tried things like desktop switching by hard taps to either side of the keyboard, but it's more of a neat gimmick than a useful interaction mode. Some (severely out of date) scripts here: http://www.thinkwiki.org/wiki/HDAPS (no HTML in comments?)
it would be cool if GMail and other data sensitive web applications used these APIs so that it would log you out of the web service if your computer had a lot of motion (e.g. someone running away with it).