Here is an example. Fred Wilson's visualization - <a href="http://weeplaces.com/fred-wilson/" rel="nofollow">http://weeplaces.com/fred-wilson/</a><p>Or Harj's - <a href="http://weeplaces.com/harj-taggar/" rel="nofollow">http://weeplaces.com/harj-taggar/</a> - he checks into YCombinator a lot.
These are really beautiful maps, and a nice game. I'm sure you're on to something much bigger with the company you're building, but many users will want to just show off where they've been all the time, and please don't take any offense if I say that this feels like "web2.0 onanism" to me.
Cool little trick and interesting to see how little I actually check in! I've heard a few privacy concerns, but if I wanted my location to be private, I wouldn't check in on foursquare.