Sorry to be posting about twitter so soon but I am working my brain around scaling issues and possibilities. Its the week of twitter and some issues have popped up.
In looking to see if anyone has tried my idea I went over to the twitter fan wiki and found a Google Maps / Twitter mashup, but it seems to only take the location in your profile, I am only seeing 3 people in Washington State.
What I want is the ability to send a txt and set your location that way. Also it would be fun to follow a geographic region,like a 10 mile radius around your zip code. Or follow everyone that is at an event, even if you are not there (SXSW). Or ignore a geo region (Leave SXSW).
This feature will come to pass. the question is where and who. Groups are coming to twitter according to Ev via Scoble.