The IRS has just released an analysis of the richest 400 American tax filers (.pdf). The top-line finding drawing the most attention is that these 400 earned about $138 billion, collectively, in 2007, the most recent year of data. In contrast, the bottom 90 percent of Americans, over 24 million filers, earned $247 billion.
One less-noticed finding in the report is that the super rich have been paying smaller and smaller portions of their incomes to taxes*. The chart below shows the effective tax rate for the richest 400 American filers from 1992 and 2007. The blue line represents the highest income tax bracket, the red line is the tax rate on long-term capital gains, and the orange line is the average tax rate that the richest 400 filers actually paid.