Gowalla, Four Square, and other similar services allow you to “check in,” and tell the world that you have visited different places. Techcrunch reports on a new feature from Gowalla:

So if you check it at SFO then five hours later check in at JFK, they know that you were on a cross-country flight and create a new graphic to showcase that, complete with your miles traveled. Below that they tell your friends about your journey. And they’re even able to see if you had a layover at another airport. … Another small addition to the Gowalla website is that they now show you a map connecting your most recent check-ins. Again, this could be interesting from a travel perspective. Imagine being able to give someone a link visually showcasing where you when on a recent trip.

In other words, for people who diligently check in wherever they go, Gowalla effectively creates a map of everywhere they go. It’s the equivalent of a human tracking device. Not sure why it’s cool, but hey, perhaps people want this. My concern is that the aggregation of this data can be used for ill. Omniveillance is on its way.