In case you have been following MBTweetFleet and availing awesome parking spaces, you would be happy to know that the service was made using an Arduino and GPS/GPRS shield.
The cars automatically generated a tweet with GPS data out of every empty parking space they passed. Via Arduino the onboard electronics were connected to a GPS/GPRS-Shield. Tweets were generated with a PHP Relay which sent the GPS-Data. This is how people could find empty parking spaces near them on twitter and even be navigated there by a linked Google map