Warning: while the above async loading code works for Twitter, it won't work for any JavaScript containing calls to document.write() as they'll append the data to the end of the page depending on the browser (or even replace the whole page!)

All is not lost though, as you can patch document.write to do the right thing and write to an element's .innerHTML or equivalent. If you are a JavaScript API provider though, please take heed and don't use document.write(). I'm looking at you, PollDaddy!