I've got about 20,000 commuting miles on my
Motorola S-10 Bluetooth headset. They're open to external sound, not sound-deadening, and in my experience they actually reduce wind noise compared to riding with bare ears. Quite durable, haven't had any trouble commuting in the rain, decent sound, and very convenient to switch automatically from music to cell phone when I answer a call.
Of course you need to be aware of your surroundings, don't zone out to music on a bike any more than you would driving a car, keep the volume low enough you can hear mechanical problems developing on the bike, etc.
As for hearing other traffic, much of my commute is on Interstate 90, I can hear all 8 lanes of 60mph traffic just fine with or without earphones, even on a rainy day.