The Pre is the first phone that I have had with real GPS support and I must say it is a lot of fun to play around with and once the SDK opens up and new applications start streaming in that make use of the support, that fun should racket up another level. Here now are some of my experiences with it to date.
GPS and Sprint Navigation essentially duplicate the functionality of a Garmin-like device in a vehicle. Providing turn by turn directions alongside either a 2D or 3D map is quite handy and having options to optimize the route for any number of criteria, including current traffic conditions is a lifesaver at times. The system can be set to call out directions over the phone's speaker can allow it to be used by drivers alone in their car and realistically can save you from buying a separate $200 GPS unit.
You can set the camera to geotag your photos based on the GPS. As we move more and more toward GPS-based information, this is going to mesh well with that. GPS also allows me to throw in a URL pointing to my current location when I use the Tweed twitter application. Again, more location-based info. I foresee that these sorts of aspects could become the main utility of the phone. The GoodFood application already can pull restaurants based on your current location, more and more is just going to be built on this information layer.
Of course, I could not write a blog post without mentioning at least one critique so here it is. The use of GPS does tax the battery a bit. I have not noticed it being a significant drain, but it obvious does not help. And you do not need to have GPS running 100% of the time. Unfortunately to turn GPS on or off, you have to go into the Launcher and scroll over to Location Services and open that up. All this time, the Pre has a handy direct drop down which gives you the date, battery life and have options to turn on or off Wi-Fi, Bluetooth or Airplane Mode. Would it have been so difficult to include GPS there as well? That would have vastly improved the efficiency with which we could manage its use.