I would guess he plays up the fussy butler image of 3po in public situations but when one on one he's normal. He definitely hams it up for the press. Knowing what we know of him now it's great to compare him to a post SW interview where he doesn't even know he's coming back for the sequel.
http://www.youtube.com/watch?v=OHjK8MAsuMQ (jump to 9 minutes in)