The geowanking community has taken notice of the Twitter service. If you're not aware, Twitter is a simple service to share what you're doing. Twitter just lets you post a line of text, and you can do it via SMS, IM, their web interface, or any number of libraries that are popping up.
TwitterMap is much more full featured. It actually polls the current public profile feed looking for "lat: lng:" specification of your current position, and then puts that on a full-frame map, with different colors depending on how long since you've updated. The problem is that Twitter has gotten very popular, and updates happen frequently. TwitterMap only polls the public list every so often, so there's a 1 in 20 chance your post will actually be grabbed.
The developer, Patrick Kollitsch is hard at work on an updated version that should fix this issue and have more features to boot.
I definitely like the idea of showing a fading history of when the person last updated, or to see a trail of their travels. Also, seeing the user's community of friends with lines linking them - especially if mixed into the history, so see as they come together and apart, would be very cool.
More to come on possible geocoding & picoformat ideas around Twitter, and like services (dodgeball, plazes, et al.)
Update (3/28/07): another TwitterMap has shown up that offers a very simple and effective interface. It also offers TwitterVision, which is a semi-realtime updating of twits as the show up and their location.