In case anyone was curious what MediaGoblin is here is a video with an overview and update on the project. It was given at a local Python user group meeting.

http://www.pyvideo.org/video/1418/mediagoblin-update

There are sites that do this for traffic and such already, http://commuterfeed.com/. Also if you wanted to do this for the subway you could just create a hashtag for your rail system. Then when ever they see a train tweet #<hashtag> train just left <station>. This would only require getting the community behind you since the infrastructure is in place. You could then use Summize to track the hashtag and populate a website so not twitter users could use it.