The US does have an expatriation tax[1] that is of concern for many. There was also a dramatic increase to the tax proposed as a result of Eduardo Saverin's expatriation before the Facebook IPO. Even though he hadn't been living or working in the US for some time prior, the US imposes taxes on all moneys a citizen earns, regardless of where they are living, or where that money was earned.
Beyond that, expatriation from the US is at an all-time high[3], and the rumor is that it's related to the adoption of Obama's progressive taxation schema.
[1] - http://en.wikipedia.org/wiki/Expatriation_tax#United_States
[2] - http://en.wikipedia.org/wiki/Ex-PATRIOT_Act
[3] - http://www.thefiscaltimes.com/Articles/2013/11/18/US-Taxpaye...