My boss's boss was using the TomTom from work & accidentally removed the SD card while it was operating. Don't know why but it crashed the thing completely. It took me about 8 hours to get it functional again (with much tech support). The repair didn't cost anything tho so all is well.
Do swap out the 1G SD card for a 2G ASAP & follow the directions for backing up the unit on your desktop.
Play with it at stop lights - not while you are driving.