Ah, the lure of all things Google...
I've been poking around in Google Maps and had some success I thought others might be able to build on. I've put this in a couple of places but thought I'd throw it here as well:
Part 1 : XML Handling
Okay, I've been playing around with sending requests to Gmaps via a Python proxy and manipulating the files returned on the fly.
As a result I've created a bookmarklet that loads the required XML file into the page: (Google Maps Load XML Data Example Bookmarklet)
If you save this book marklet and click on it when on any (?--certainly the home page) Gmaps page it should move you to a location in Vancouver, Canada.
By changing various values you can do some more experimenting... For example, I have successfully added another 'location' tag with an id 'B' and new coordinates. Also I changed the marker image to be a random png from the Google site--but discovered the image dimensions seem to be hard coded so it was distorted."