Have a Bluetooth communication (Sena) so my wife can communicate AT me when she rides (gerbil bladder). Other than that annoyance it also interfaces with my gps, phone, and ipod if I bring it. Not big into music while riding - I start getting into the music at the cost of paying attention to the road. My fault I know, so I rarely listen to music.
The Bluetooth is great though, music works super and phone use is seamless (I ignore - why ruin a good ride) plus if you turn on GPS volume it gives you turn by turn directions for the rare times you are actually going somewhere.
Hate hearing another bike with the stereo blasting, get enough of that when I go into town and see all the cages in traffic.