UPDATE: below. And MaxedOutMama continues the discussion here.
I repeatedly have shown that the upper income brackets pay the lion's share of Federal taxes, and also that top earners pay higher tax rates. Confirmation comes from the Congressional Budget Office, "Data on the Distribution of Federal Taxes and Household Income":
source: CBO, April 2009
The chart on the right demonstrates that only the highest income quintile pays more in taxes than its share of income, which depicts the "progressiveness" of U.S. Federal taxes. See also Tax Foundation (2007 data).
CBO also tracks historical tax data; here's the trend of total effective Federal tax rates (including income, social, corporate and excise) by income quintile from the beginning of the Reagan Administration through 2006:
source: NOfP Chart via CBO data
Note that tax rates have dropped among all quintiles, but while the top quintile rate is down only 1 percent, all other quintiles show much steeper declines--including halving the tax rate for lower quintile earners. Indeed, in 2009, almost 47 percent of "tax units" (filers) -- mostly in low income quintiles -- paid no or negative Federal income taxes.
So why do lefties claim the rich don't pay enough and want to increase top quintile tax rates? Cause, in the self-described "reality-based community," rhetoric trumps reality.
Extensive discussion in comments, including MaxedOutMama's linking to the 2008 quintiles, and the income per-quintile.