We started our little service that adds geo location information to single Twitter status messages.Unlike other services this is done by a tiny URL that contains the whole geo location e.g. http://GE0.at/0MbEX8 which describes the Eiffel Tower in Paris. This is achieved by a modified ‘geohash’ algorithm (more on that at Wikipedia).
The second unique feature is that users can follow places in a similar way than they are used to follow users on Twitter. Therefore the earth is divided in discrete squares of about 0.25 square kilometers. You can keep updated by subscribing to a RSS Feed or visiting the web site.
An iPhone application is also ready but not yet approved by the Apple App Store. In the meanwhile you can watch a little demo on the web site under the ‘iPhone’ menu entry.