If you have lots of friends that you like to keep track of for meet up or just to satisfy the voyeur in you, Google Latitude has landed for the iPhone. The Latitude service was first offered as a web-based application only and after sneaking out for a short while last week it is now on the App Store for you to download.
The app lets you share your location with friends that want to follow you using the map service and you can do the same with them. The idea behind the app is that you can find where your friends are and then follow the maps to meet them if you want. I can also see this app being something that parent who wants to know where their kids are being able to use this for tracking purposes.
If you are the privacy type, you can set the app to not update in the background. As it is, the app automatically offers up your location data even when your phone is locked and the screen is off. You can turn that feature off if you want so you only share your location say on a Friday night when you need people to hang out with. The app can also be set to show only your city not the specific street where you are.