The supporters of tax cuts and those who claim that US taxation system is fair points to this graphic which shows that the share of income taxes being paid by the richest 1 percent has increased sharply over the past three decades and they now pay (40.42% of total federal income taxes in 2007) more in federal income taxes than the bottom 95 percent...
... But his conceals the fact that the share of the income of the bottom 95% has been continuously on the decline and the incomes of the richest Americans have experienced much greater growth.
David Cay Johnston looks at changes in the tax burden for high income and lower income taxpayers in the US since 1961 and finds that 90% of the population did not do well over this time period. He also argues that America's tax system is breeding deep problems by redistributing benefits to the top while maintaining burdens for the rest of Americans.
Update 2 (24/2/2011)
Excellent post in Economix on the tax rates paid by the residents of the Helmsley Building - the poor (janitors and other workmen) pay much more in taxes than the multi-millionaire residents of the building.
Update 3 (22/6/2011)
Bruce Bartlett has three posts, here, here, and here, where he discusses the low level of federal taxes as a share of the gross domestic product in the United States, both historically and in comparison with other developed economies.
Update 4 (18/8/2011)
Graphics here about the low level of corporate taxation in the US in relation to the rest of OECD economies.