You're right, enomar; I've updated the post to reflect Google's recommended placement of the asynchronous snippet (and your other comment regarding the script type attribute only defaulting in HTML5).
Perhaps instead of appending to document.body, it would be better to use document.documentElement.firstChild to use the head element instead (this is what is present on http://diveintomark.org).
That isn't true for Google Analytics. It's designed to be placed at the bottom of the head section: http://code.google.com/apis/analytics/docs/tracking/asyncTra...