I am not sure how google latitude works but i have got a really basic idea, which can help in finding a way to your friend or help him find a way to you or to some other place.
Idea: Now a days almost all midrange phones have GPS module inbuilt. Once the phone has some kind of internet connectivity, the guy will store/update its location every minute on it or may be at every thirty seconds. Now where this location will be stored on net. For that i am thinking of a simple way – goole docs. I do not want to have a dedicated server so i will use google account of all the users and have a shared google doc between them and have the location details stored there. It can store all the history a well as some routes which you have travelled earlier.
Thats it, implementation is remainig. I really want this to be implemented..