I've recently been using Waze, I tired it originally on a 3G phone and found it to be useless but with a 4G phone much better (YMMV - a friend who recommended it said he had not trouble with it on 3G)
I've not been able to contribute much back though as I don't like touching the screen while driving - too distracting. I guess it is monitoring my speed, location and progress though.
I wonder when and how it is going to be monetized. Quite like it though so far.