People who pay no more than $802.50/yr in Federal tax only for the 2008 tax filing season:
Married, earning $25,925/yr (3% effective tax)
Single, earning $16,975/yr (4.72% effective tax)
Single with one eligible child, earning $30,425 (2.6% effective tax)
Married with one eligible child, earning $39,425 (2.04% effective tax)

Of course, those that are married and earn a meager $17,900 do NOT pay federal taxes anyway (as of the 2008 tax filing season … which is filed by April 15th, 2009). The reason for this is that they may pay taxes throughout the year, but they will get it all (and possibly more) back when they file their taxes.
Add in one eligible child, and they can earn up to $31,400/yr and not pay one penny of Federal tax. That is because of the basic deductions:
$10,900 for being married (this is the “standard deduction”)
$3,500 * 3 = $10,500 for personal exemptions
$10,000 additional income for an eligible child … at the 10% tax rate.

So, basic math shows us that
$10,900
+ $10,500
+ $10,000
———
$31,400

Of course things are a lot worse if you’re a single parent with 1 eligible child. You can only earn: $5,400 + ($3,500 * 2) + $10,000 = $22,400

That is before they pay 1¢ in Federal income tax.

I am middle-class on an income level, and have no capital gains taxes, or AMT.
With that being said, because of deductions (mortgage interest, property taxes paid, 4 dependents that are under 17 in our house), we paid 2.9% taxes last year.
That’s the REAL tax that we paid (otherwise known as “effective tax rate”, although we are in the 25% tax bracket.