We've seen the 3G iPhone's GPS in action in a number of ways in Build 5A292g of the beta 2.0 Software Update. It can mark your location on a map, and will be utilized in the Camera app as well so you can take precise pictures of an area and send them online with geo-tagging information such as height and length -- a feature we've seen before in Google Earth and Maps, but never this tightly integrated with a phone.