You may have made a mistake in your calculations, or there could be a problem with the particular instructions you're referring to.
I examined the draft "Recovery Rebate Credit Worksheet" for Line 70 of the 2008 Form 1040 (draft). This Worksheet is found within "2008 Instructions for Form 1040 - Draft Worksheets & Tables", available here:
http://www.irs.ustreas.gov/pub/irs-dft/i1040gi--dft.pdf. See pages 18 and 19.
I see no indication that a negative number is to be entered on Line 70. Therefore, we will
not be taxed on the Stimulus Tax Rebate received earlier this year. If the taxpayer received the full Stimulus Tax Rebate, then there should be no impact on their 2008 tax return.
If the amount on Line 29 of the Worksheet is
zero or less, then -0- should be entered. Thus, no impact on taxes.
If the result on the Worksheet is greater than zero, then that positive number is to be entered on Line 70. This indicates that the taxpayer is entitled to a larger Stimulus Tax Rebate than they actually received, and the extra amount they're entitled to will be refunded via the 2008 tax form. This is the case for me personally, since we (a married couple) paid only a minimal amount in tax for 2007, so we only received a $600 rebate check (most married couples received $1,200). We owe slightly more than $600 in taxes for 2008, so we'll be receiving the additional rebate amount we're entitled to as part of our refund when we file for 2008.
If the taxpayer happened to receive
more rebate money than they were entitled to based on the 2008 tax return, they DO NOT have to pay back the difference. Consider it a gift from Uncle Sam.
Please correct me if I'm wrong about this, but that's how it looks to me.