I just gought the Treo 680 today. I am fascinated by this device. what an improvement over my Treo 650 - i can actually run Goodlink and TomTom 6 at onece.
There is a fix provided by Palm for Treo 680. It is available at:
http://www.palm.com/us/support/downloads/gps_nav.html
They also have the fix for Treo 750 there. I applied the fix on my Treo 680 and Voila!
Good Job Palm and TomTom!