Funny you should mention that. I got trooped last week. He came up to the bike ranting at me. I held a "just a moment" finger at him while I turned off my Zen (into my Etymotics). Though for sure he was going to read me my rights. Anyway, I got the lecture, never took my Symax off (just flipped the front up), and apologized for not following the law and generally being a dumb ass.
He did NOT say anything about the ear phones or radio. Of course in Indiana there is NO law about earphones or plugs. Not much law in those grey areas at all. I DO know that there are laws against speeding, not signaling, not yeilding, wreckless driving and endangerment. Merry Christmas, though (Dec 26th...).
I was happy to find out that I could have a normal conversation with the nice troop with my helmet on and my plugs in (xm off). And I know I can hear sirens and such. And boom boxes. And bass woofers from lo riders...etc...
When I come out west, I'm riding with my full audio hookup. If I get ticketed, I'll pay it (maybe) and keep right on going.
Plugs in and tunes on!