Further to my earlier post, it turns out that there’s already plenty of work under way on hacking Google Maps. Engadget has a how-to on adding your own annotations to Google Maps — it requires Firefox and a plugin, though. This page shows you how to run Google Maps off your own server with your own custom XML data. This is a more general page on Google Maps hacking and bookmarklets. And there are a couple of wiki pages about Google Maps hacking — one for hackers and one for users.