I am just checking out the Shibuya area twitter map which shows those people who are tweeting locally with a GPS enabled device. As more people use applications requiring GPS, this map will start to fill up with thousands of tweets.
It is another interesting example of how search on the internet has changed from corporate encyclopedia type entries, to news items, personal opinion blog posts, to twitter-like snap shot comments, and then to take that information of the page and reorganize it not just into subject matter but also source of origin.
Do you have a twitter map website you can share with us? Are you on the map somewhere?