On a J-1 visa you may have to return to your home country for 2 years after it expires -- you can only visit on tourist/student visas in those two years, not work in the US. I was subject to this, as a UK citizen interning in Redmond between undergraduate years (in 2002), but I have not met many other J-1 holders and don't know how common it was.
http://internationalaffairs.uchicago.edu/page/j-1-status-two...