mbs: The new law creates a new bottom tax bracket with a 10% marginal rate. For a couple it covers the first $12,000 of taxable income (AGI minus your deductions and exemptions). Since this is a reduction from 15%, if you have at least $12K of taxable income, your savings are $600. The $600 check you get next month is an advance on the tax cut you will realize next April when you file for 2001 (if you have $12K or more taxable). It is not a one-shot deal. It continues as long as you have enough taxable income, or until the law is changed.
Over 30 million taxpayers don't have enough taxable income to get any benefit from this, and about 20 million more will get less than the $600 ($300 for a single person).
Check out the two most recent articles on The American Prospect web site by "Taxonomist," for details. (www.prospect.org)
The way the new law is phased in, it happens that the benefits ordinary folks get come first, while the bulk of the benefits for others are phased in. This makes them a vulnerable political target, since the likelihood of the law being significantly altered before it completely takes effect is absolutely certain.