stonyarc, I have a Googlemap vbulletin plugin in my forum too. It's a little different from yours:
1) it uses Google Map wrapper class for google map API: PHP GoogleMapAPI
http://www.phpinsider.com/php/code/GoogleMapAPI/
2) it has the of geocoding ability (the ability to convert a street address to latitude and longitude , for example support a Canadian Postal Code or Address for eg. M2J 3R7 or 277 Wellington Street West Toronto )
3) it supports query information by distance.
you can see these functions in this website:
http://www.iask.ca/
I am not sure to release this as a new vBulletin plugin, do you like to intergrate them into your code?