In Highest Income Earners Pay Most Taxes, the National Center for Policy analysis lists some interesting IRS data:
The data show the distribution of the tax burden by income group, or, in other words, the share of total federal personal income taxes paid by each income group:The top one percent paid 34.75 percent of federal personal income taxes. [...] To rank in the top 1 percent, you had to report adjusted gross income (AGI) of $269,496 or more.
The top 5 percent of taxpayers paid about 54 percent of total personal-income taxes and had AGI of at least $114,729.
The top 10 percent of taxpayers by income had AGI of $83,220 or more. The top 50 percent of taxpayers had AGI of at least $25,491. The 4.21 percent share paid by the bottom half of taxpayers was virtually unchanged during this period.
The top half paid almost 96 percent of all income tax. Wow.