Just wanted to save this and share, I'm doing some mobile development at work and I found a great Firefox plugin that let's me fake out my location. It's called GeoLocator (https://addons.mozilla.org/en-US/firefox/addon/geolocater/)

It has a map based interface, developed using Open Street Map - You simply drop a marker on a spot and name it, or search by address - You can save as many points as you want and switch between them at will - this geolocation data is in turn fed back to your app when you make a javascript request for the current location of your computer.

It's pretty awsome for early testing on location aware HTML apps.