A few quotes from the article This Fact May Not Sit Well: Americans Are Under-Taxed by Kevin G. Hall, McClatchy Newspapers make the point.

Americans on average saw 17.3 percent of their income go to federal taxes in 2009 and 2010. The last time the percentage was this low was 1975, and during the late 1960s.

If you exclude social insurance taxes on wages – for Medicare and Social Security – the share of taxes as a percentage of income drops to 9.4 percent in 2009 and 9.3 percent in 2010, the lowest since 1950.

“It’s hard to argue that we’re overtaxed, and we’re low by world standards,” said David Wyss, the chief economist for the New York ratings agency Standard & Poor’s.