The 400 taxpayers with the highest adjusted gross incomes in the United States made, in 2006, on average, $277,444,330 (in inflation adjusted 2008 dollars).
By comparison (in inflation adjusted 2008 dollars) the comparable numbers were:
2002 -- $122,872,340
1997 -- $123,142,970
1992 -- $70,843,660
The bulk of the incomes of the higher 400 AGI taxpayers are unearned. In 2006, the average top 400 AGI taxpayer received 63% of their AGI from capital gains, 7% of their AGI from dividends, and 8% of their AGI from interest. Thus, 78% of their income comes from these three sources of unearned income. Other sources of unearned income, such as rental property income, were not broken out separately, so average earned income is an even small percentage of the total.
The average tax paid by these taxpayers as a percentage of AGI is 17.2% (lower than any of the previous time periods), largely as a result of tax preferences available for capital gain and dividend payments.
The figures do not reflect income which is excluded from income entirely under the tax code, the most material of which, in this tax bracket, is non-taxable municipal bond income.
The figures also don't distinguish between compensation in the form of stock options and fund manager interests that are essentially bonus compensation for services, but are treated as capital gains for tax purposes, and capital gains that are a function of gains on investments purchased for cash by third party investors.
The slight slip in inflation adjusted returns between 1997 and 2002 reflects the tech bust. The 2006 numbers, of course, do not reflect the collapse in the capital markets in 2008.