“The Universal Edit Button is a green pencil icon in the address bar that indicates a web page is editable. It is similar to the orange “broadcast” RSS icon that indicates there is an RSS feed available.”
I love this: the idea that you can edit this page should be a regular part of browsing the web, just like subscribing to a podcast or blog. Expect to see this on Appropedia soon.
At the moment you need a Firefox extension to be able to see the button in your url bar, but in time, enlightened browser developers will integrate it in their code.