[celticjames]

Good point. According to wikipedia (http://en.wikipedia.org/wiki/American_diaspora) there are 6.3 million Americans living abroad or ~2% of Americans. So perhaps ~0.04% of Americans abroad renounced citizenship annually. To put it in context, though, you'd need to know how that rate change over time and the size of the American diaspora over time.

So it's hard to judge how big or meaningful this story is. But anecdotally, I too am in Canada and I have definitely been hearing a lot recently from American friends who are finding US citizenship to be a PITA because of taxes.