To the many willfully innumerate journalists who have written about the subject, Warren Buffet's mistaken claim that he pays a higher tax rate is enough to prove that we have to raise taxes on millionaires, where millionaires are those who earn over $250,000. Here's a collection of useful links that present some inconvenient truths about taxes and inequality:
Clive Crook: U.S. Taxes Really Are Unusually Progressive
Greg Mankiw: Five Observations About Progressivity and Tax Rates for the Rich and Poor
James Pethokoukis: The Chart That Closes the Case on the Inequality Myth