There was a study (German I believe) on impacts to the head and face from motorcycle crashes (someone had posted the illustrations earlier). The study showed that the majority of impacts are on the front of the face and chin. Personally, I like my jaw and teeth. I recently cracked a tooth on a piece of gristle from a slice of sausage. I may need a root canal, and its difficult to chew on one side of my mouth. I figure that's nothing compared to having my jaw shattered and teeth broken.
I'd say go full face. Try different types to make sure you can hear well. I have no problems hearing on mine -- sirens, horns, etc. My wife just needs to speak up when we're riding together, but that's just to he heard over the sound of the wind. I see too many riders around Philly (PA has no helmet law -- go figure) riding motorcycles and scooters without a helmet, or even a brain bucket, in flip flops or sandals. I figure they're single or without an immediate family to be taking such risk.
In colder weather the full face protects you from the cold and wind. Can't imagine doing my commute in anything else.
-Wolf
