How the Tax Burden has changed (since 1980) -
... This is a very good article with several interactive charts that show how the tax burden has changed since 1980.
The final chart at the bottom of the article shows the ratio of share of taxes paid over share of total national income. It shows how the top income brackets ratio of share of taxes paid to share of national income has gone down since 1980.
The first chart you'll see shows the "Share of yearly income paid in federal, state and local taxes, by income bracket". It shows how the taxation rates for those making above $200,000 a year have gone down about 13% since 1980, while the taxation rate for those in the $50,000 to $75,000 income range has gone down about 6.7%. Total tax rate for those in the $75,000 to $100,000 income range has gone down about 7.9% since 1980.
http://www.nytimes.com/interactive/2012/11/30/us/tax-burden.html
In a progressive system, upper-income households pay a larger share of taxes than their share of income, while the opposite is true for lower-income households. Over the last three decades, taxation in the United States became less progressive.
Households earning more than $350,000 paid 20 percent of the nations taxes in 2010, 1.37 times their share of total income, while in 1980, those households paid taxes equaling 1.56 times their share of income. The change was larger before the recession, which reduced investment income, as in past recessions.