Apple's latest iOS brings enhanced location services to your iPhone. So enhanced that some apps make it seem a little bit scary at just how well they're tracking you, even when the app isn't running—but it's a good thing! Right?
A small, but interesting note: Apple's published an "App Store Tip" for developers that it'll reject apps which "use location-based information primarily to enable mobile advertisers to deliver targeted ads based on a user's location." It's not to protect you.
Remember how the first gen iPhone (and similar non-GPS devices) use Wi-Fi nodes to guesstimate the user's position? Snow Leopard will do that, too.