The U.S. tax system is somewhat progressive. Income taxes, especially, are progressive, slightly more than offsetting regressive taxes such as Social Security and sales taxes. Therefore, I would expect that the percentage of tax paid for any given individual on this board, whose membership seems to be a good bit wealthier than the average household in the U.S. (where Average Household Income is $50,221) would be somewhat higher than the average.
But the total tax burden in the U.S. as a percentage of GDP is 27.1%. So when you take all the poor who pay a good portion of their income in sales taxes and payroll taxes, average with all us millionaires, the final number has to come out to 27.1%. There can't be many 60% folks in the deck, or that average won't work out.
Average household income source:
http://quickfacts.census.gov/qfd/states/00000.html
Likewise, it is not relevant what our tax rate is in the abstract. The relevant inquiry is what it is in relation to other countries who are similarly situation to the United States and with whom the U.S. is competing. Clearly, out taxes are very low (as are our government services) compared to comparable countries.
And clearly the much lower taxes that we (and Japan, Korea, Mexico, and Turkey) are enjoying aren't doing us much good economically. Otherwise, we'd be beating the pants of countries like Germany, France, Finland, etc. who are kicking our ass all over the place economically.