Instead of April 15, the deadline is April 17 in most states, and April 18 in six states -- Maine, Maryland, Massachusetts, New Hampshire, New York, Vermont, and in Washington, D.C. -- whose residents file to the IRS center in Massachusetts, where Patriot's Day will be observed Monday.

Last year, the IRS processed about 132 million income tax returns, and brought in nearly $2.27 trillion in total tax revenue, a 7% increase since 2000, and about equal to the GDP of the United Kingdom. Individual income tax revenue amounted to $1.11 trillion.

Here's a look at who pays taxes in the U.S., and how much they pay.

The tax burden: No one likes to pay taxes. But in comparison to other developed countries, and to the recent past in the U.S., American taxpayers have a relatively light tax burden.

Government at all levels collected taxes equal to about 26% of the U.S. economy's total output last year. That is less than the tax take in most European countries. Sweden has a tax burden of about 50%, according to the Organization for Economic Cooperation and Development; Germany has about 36%. Japan has a tax burden roughly equal to that in the U.S.

Moreover, federal taxes amounted to 17.5% of gross domestic product, up from a modern low of 16.3% in 2004, but well below the high of nearly 21% in 2000.

But keeping the tax burden low will be difficult. Last year, the federal government's spending exceeded its tax take by about $318 billion. And the retirement of the baby-boom generation starting in 2011 could cause spending on big-ticket federal retirement programs to jump.

Tax distribution: The U.S. tax system continues to be "progressive," which means that people with high incomes generally pay a higher percentage of their income in taxes than those with low incomes.

Currently, the 1% of American households with the highest incomes -- those earning an average of about $1 million a year -- pay about 31% of their income in federal taxes, including payroll tax and income tax, according to the Congressional Budget Office. The 20% of households with the lowest incomes -- those earning an average of about $15,000 a year -- pay less than 5% of their incomes in taxes.

That tax system is modestly more progressive today than it was a quarter-century ago. In 1980, households in the bottom 20% of the income distribution earned 5.7% of all income and paid 2% of all federal taxes; in 2003 -- the most recent data available -- they earned 4.2% of all income and paid 1% of all taxes. Meanwhile, the highest earning 20% of households earned 45.8% of income in 1980 and paid 56.3% of all taxes. In 2003 those high-income households earned 52.2% of income and paid 65.7% of taxes.

The Bush Tax Cuts: One reason for the relatively low tax payments is a series of tax cuts enacted by President Bush and Congress starting in 2001. For those in the bottom fifth of the income distribution, those tax cuts were worth an average of about $18 a household last year. For those in the top fifth, the tax cuts were worth an average of $4,845, according to the Urban Institute's Tax Policy Center.

But most of those tax cuts are set to expire in 2010. Mr. Bush is pushing to make them permanent. But many in Congress, including some Republicans, are worried about the effect that will have on future budget deficits.

The federal estate tax is particularly troublesome in this regard. Under current law, this tax is set to disappear in 2010. But then in 2011, it returns to the same levels as before the Bush tax cuts. Congress has been struggling with whether to tinker with the tax, or eliminate it entirely, amid concern about budget pressures.

Do you have to pay? The Internal Revenue Service says every year hundreds of taxpayers try to get out of paying taxes by making various claims. Among the most common: "The 16th Amendment is invalid" and a "taxpayer can refuse to pay taxes if they disagree with the government's use of them." Don't try it. The IRS says none of these arguments wash.

--Compiled by Lauren Etter

Commentary:
The WSJ is still unable to admit they were wrong. The Bush tax cut was based on a the lie - surpluses and has already cost us $2.6 trillion in new debt. This was after Bush promised to pay down all our debt. Bush is either a liar or a failure. The WSJ supports his failure and lies. The largest accumulation of debt in human history has occurred under Bush. Every tax cut adds more debt to the $8.3 trillion of debt. Over 80% of all our debt has been created since the Reagan tax cut.