Having suffered years of expensive advice about international taxation and other malarkey: US citizens have been subject to tax on worldwide earnings for quite some time if your foreign *earned* income exceed a threshold, currently around $100K, or any amount of non-earned income. Elsewhere if you're a tax resident or repatriate money you'd expect to be liable at least for the difference between the tax you paid abroad and the local tax: the US difference is that you don't have to be US resident or repatriate the $ to owe US tax.

All I know is my own experience. When I filed my taxes in 1999, I had earned some income in the US for which I paid taxes in the US. Because I passed the physical presence text for the income that I earned in the UK, I only paid taxes for that income in the UK. When I filed my taxes in 2000, I had no earned income in the US and did not pay any taxes there, having met the physical presence test for that year.

Let's get rid of all these complicated tax laws and put the IRS out of business ;)