Finally! Someone has answered the all important question.....

(Rebates start going out today...)

Your stimulus payment is a one-time tax cut - an advance on a credit you'll receive on your 2008 return. You will not owe tax on your payment when you file your 2008 tax return, and it will not increase the amount you owe or reduce your 2008 refund.

The stimulus payment is based on your 2007 income initially. If it turns out that your 2008 income and number of children would have qualified you for a larger rebate than the one you received, you'll be sent the difference. If it turns out your 2008 income was lower than in 2007 and you should have gotten a lower rebate, you get to keep the difference.