i use headphones for boring commuting stuff, i dont have any music on that could ramp me up, its not mellow im just hard to ramp up(one of my lower skill level good friends uses music and starts to rock out, makes me extremely nervous).
the earbuds go IN my ears and work like poor earplugs, but i keep my ipod in my jacket pocket so i can just pause it super quick if i need to actually focus on something.
earplugs for sure at track, even on the supermotos and minibikes im for earplugs.
have a chatterbox on one of my helmets, never use it, sound quality sucks for music becuase there on top of your ears and its not good enough for cell phone convo, which i hated trying anyway because it made your commute feel like you were just gaiming with your buddy.
and helmet quality isnt the deal, im using 2 different commuter helmets right now, ones arai, ones KBC, one for night and one for day, another for track(arai), and another for supermoto(shoei) and mini(the same kbc). not to say helmet quality doesnt help but its about being used to the random irrelevant noise being deadened for you. its just unnecessary hearing dmg, but dont take my word for it... i wear headphones and thats worse then nothing.... boring.