Well, for now (On Linux) it only offers canned operations for XMMS. This will expand in the future though. In windows, you can pretty much use it to emulate key bindings for various applications.
I have mine mounted above the rear-view mirror, and I love the control for scrolling through the playlist, play/pause, and volume control. More info, and the plugins new home is @
http://groomlakelabs.com/grandamp/code/
It is much better than attempting to use a touch screen while driving
I am still updating my site with respect to GrandAmp v2.0 (My newer install) and I will be doing pictures soon... Hope this helps!