I've been playing with a mapping website called 'frappr'. Essentially the idea is that people can add themselves to a map - the maps might be groups of friends, groups of people who like bunnies, or anything. Out of curiousity, I made a map for people who read this site (the map is here.
If you're not on the current map view, you can scroll the map around, and zoom the map as appropriate.
(I've also found ballofdirt.com - which looks very useful).