I believe that was the passenger side NAG switch. It activated the passenger ejection seat when the nagging got to be too much for the driver. It only came on the James Bond edition Georgetowns.
Seriously, I tried to do a search in the Georgetown forums for maybe a similar question.
I did find this one where Fred says the toggle switch is a mirror defroster for his 05 model in this thread, so Bubbles may be the winner of this round of jeopardy:
Dashboard Battery Boost Switch
If you do confirm that's what it is, let us know please.