GPS technology has suddenly gotten really cheap, and I've taken advantage of it in 2 big ways. First, I managed to get a GPS watch from woot.com for a great price, which includes the arm-mounted GPS receiver, for urban running. It's so accurate, it provides miles per hour in real time while you are running. The other cool use of GPS is the updated version of Microsoft's Streets and Trips. This mapping software used to be nice-to-have for road warriors, now it has moved to essential because it includes a small GPS receiver. You arrive in a foreign city with only the hotel address, punch it in, and you have turn-by-turn directions, spoken via your laptop's speakers, with the traced-out route on the screen. Having Streets and Trips on a laptop is better than having one of the little Palm-sized units because a) I'm taking my laptop with me everywhere anyway and b)the screen on the laptop is much bigger and nicer. The only downside is that you've got to be within a couple of hours of your destination or have a car adaptor for your laptop.
GPS has reached the point where it is cheap, available, and plentiful. My friend Scott Davis has a nice keynote presentation at No Fluff, Just Stuff this year where he argues that location based services will be very important in the near term. The combined technologies of cheap GPS, mashup applications that leverage tools like Google maps, and the growing awareness in software of actual location suggests rich applications beyond what we've got now. If we can just get all this down to the phone level, the only thing left will be flying cars.