Done a quick forum search for the URL of this frankly amazing little tool and got nothing - it was only a couple of weeks ago that I e-mailed google to ask them to sort out some sort of travel conditions and speed camera wiki component to overlay locations of heavy traffic and speed cameras on their maps...
...turns out it already exists at http://www.dynamite.co.uk/local/ (hint - select what you want to overlay from "select dataset" and then click update data whenever you move/zoom on the map)
Hope this is useful to someone