I’ve been a fan and user of Google Latitude for a long time. The privacy settings are nicely tunable, the maps excellent, the friend-view is usable and the locations and location reviews are nicely up to date.
Jonathan Green pointed out a short while ago that the latest update to Google maps includes a check-in points system which new adds fun to the excellent package. I’m not quite sure how the points system works and how the leaderboard is formed but I like what I see.
With Google Plus taking off there’s huge potential for this to grow quickly. I suspect that Google will roll latitude friends into a new circle. A live ‘people in my area’ circle could be fun too. Viewing live Plus entries on a map (as one used to be able to do with Googles Buzz service) is also going to be interesting.