As a matter of course around 1,100 persons per year renounce their U.S. citizenship every year for a number of reasons. Recently that number has ratcheted up significantly.
via Reuters :
Last year, almost 1,800 people followed Superman’s lead, renouncing their U.S. citizenship or handing in their Green Cards. That’s a record number since the Internal Revenue Service began publishing a list of those who renounced in 1998. It’s also almost eight times more than the number of citizens who renounced in 2008, and more than the total for 2007, 2008 and 2009 combined.
The United States is one of the only countries to tax its citizens on income earned while they’re living abroad. And just as Americans stateside must file tax returns each April – this year, the deadline is Tuesday – an estimated 6.3 million U.S. citizens living abroad brace for what they describe as an even tougher process of reporting their income and foreign accounts to the IRS. For them, the deadline is June.
Republican Congressmen and GOP primary presidential candidates have repeatedly called for tax reform  through passage and implementation of the flat tax. For Americans renouncing their citizenship, those reforms aren’t coming fast enough.