is it possible? Sure, probably. Maybe. Some of that, maybe. is it easy? 
No. Because the arduino and most every other AVR board I've seen isn't designed to be a USB HID, that means you have to run everything through the virtual serial port. As far as i can tell, this is really great if you want to program specific things in the sandbox type environment of Processing, flash, max/MSP, no problemo.
Now, maybe someone can chime in on integration with what flash, max/MSP, PD can do to system level controls... my guess is that there's going to be limited control of the system from these environments for security's sake.
You might be better off buying a cheap USB multi-button mouse, tearing that apart and rewiring the buttons to whatever other switches or buttons you want... I know logitech has some fancy things you can do with the buttons on their mice.. there's a system prefs pane that will let you do some limited things...