I 've just read about Adidas Run Tracker, a mobile application made especially for the London Marathon, were the spectators could track their friend who took part at the marathon. The athletes shoes were equiped with RFID chips and so the system was able to know where the athlete is. Then this information was propagated to the specator via SMS and WAP.
Nice idea I suppose and implementation.
The idea was simple, the spectators want to know where their friends are and meet them at some checkpoint, encouraging them.

Read the full article here.