I was going through some drawers and stumbled across my good old Griffin PowerMate that I got back before I started using Linux. It controlled iTunes in Mac OS 10.1 and was great because I could change volume and pause music without having to change programs or anything. These days I use Rhythmbox in Linux to listen to music and theres not a plugin for it. Yet!
Rhythmbox supports plugins written in python, a guy has some skeleton python code for talking to the powermate, and that means something could work out!
I got the powermate working by compiling and loading the powermate module for 2.6 linux kernels (In 2.6.23 it's in Device Drivers -> Input device support -> Miscellaneous devices -> Griffin PowerMate and Contour Jog support), adding a udev.d entry:
I plugged it in, catted /dev/powermate, and with each twist or push it spit out garbage to the screen. Success!
A quick glance through everything shows that Rhythmbox doesn't support threads and the python code here uses polling so I'd need to delve into the Rhythmbox docs to figure out the best way to do that, but Rhythmbox also exposes itself through DBus and there are some examples of using this around the internet. In a few minutes, I hacked together something dirty to cover the basics and perhaps later on I'll make something that works as a Rhythmbox module. Right now pushing the button is play/pause, turning it adjusts the volume, and the LED shows volume when playing and pulses slowly when paused. Here ya go: