Google Latitude looks great on the iPhone
The iPhone Latitude experience is pretty smooth. Adding friends, approving requests, and changing privacy settings were all extremely easy. Privacy is adjustable for each contact you add: you can show your specific location, just your city, or nothing at all. Latitude can also update your location automatically or manually, depending on your preference.
Sure, you can be sour that Latitude is web app and not a native iPhone app, but it's a really well-done web app. Besides, a Latitude iPhone app would likely have been rejected by Apple for overlapping functionality with Apple's built-in Maps app (which happens to serve Google's maps).