regarding VU meters, my interest is more along the lines of having the arduino front-end an actual set of meter movements, real cheap ones, like these from ebay:
the idea would be the arduino would sample the audio and do the correct VU rise/fall time decays and send the 'math output' to the real meter movement in the form of a dc signal (maybe filtered pwm, maybe something better). you could also show peak or average and its 'just math' and the meter does not really even matter anymore.
I have not gotton around to writing the stuff to really emulate a true VU meter. that's what I was hoping to see. its rare to find VU meter code, for some reason, and even good hardware schematics are few and far between (again, for true-to-spec VU meters).