Built in GPS gets +/- 40 meters in an urban canyon like SF (i.e. worst case). I think for all intents and purposes GPS will get you 97% there for 3% of the effort as any of these other methods (which probably aren't implemented anyway).

In the real world (with signal problems, battery problems, and a skyhook database with inevitable errors) GPS is unfortunately not quite that good. I really wish it was though!

i'm basing my numbers based on my experience when I was at yelp - which always presumed a real GPS signal and not using any skyhook (or at least not only using skyhook).