Exploring Google\'s +1 Button, I found two things odd about the code they supply:
The first trick is interesting. It looks like a creative way to pass "global" arguments from the page markup to external scripts. There are ways to find the element that sources the code that's currently running, and I would not be surprised if the inner text of that
element was accessible from the DOM even though the browser ignores it.
In your question, this pattern allows each external client-side script to use (at least) its own localization settings, and also allows server-side code to render that parameter as a side effect of rendering the element itself. That's impressive.
The second trick, I'm not so sure about. Basically, I think most browsers would consider the namespaced
element as unknown or even invalid, so they should render its content, but it won't do anything, of course, since that element is empty to begin with.
However, client-side code might still be able to match the namespaced element using DOM navigation, and replace it with its own generated content.