When the Bush tax cuts went through, there was a provision to get back some of the overseas money. That jump brought it to $250b in 2006 (http://www.nytimes.com/2006/07/09/washington/09econ.html?pagewanted=all), and I've seen somewhere that it was closer to $400b in 2007. I don't think that number really changes much in regards to it being worth the trouble of collecting, considering the externalities.