As part of the ongoing T-Mobile G1 review, let's start with the G1's unique features. First, let's acknowledge that the G1 is like any Google product: beta. It is far from seamless. But its perpetual internet connection, compass, GPS, and camera allow it to do some interesting tricks. Let's enlist a little hyperbole.
Clairvoyance. When Google unveiled Android, the showstopper was their demo of StreetView. Google Maps had recently added StreetView to the desktop, allowing you to select a location and see a 360-degree photo of the location. You could pan it with the mouse to look at what your destination looks like. It was like clairvoyance. Android took that one step further: view street view with the compass on, and as you physically move the phone around, the photo pans. North in the photo is north. I have tried out this feature and it's fantastic.
Omniscience. But suppose you're visiting San Francisco and you want to know more about the local landmarks. Install and start Wikitude. The app uses GPS to figure out where you are and the compass to figure out where you're pointed. Then it lights up locations on the map with descriptions pulled from Wikipedia. But the real payoff is in Camera View: you see the real landscape through your phone's camera, and the landmarks are overlaid over the landscape. It's like Luke's binoculars in Star Wars.
Maybe you'd rather look at the stars. SkyMap takes the GPS and compass data and displays a 3d view of the stars, planets, and constellations. If you've wondered if that bright star is really Venus, you can compare the star map with the sky. And if you want to know what stars you would see if the Earth were transparent, just point the phone toward the floor.
These two capabilities are just the first of many exciting ones that the G1 brings. Which is great, because the G1 is a wonderful mobile internet device, but not a great phone. More on that later.