According to the IRS:

Q. Is my stimulus payment taxable?

A. No. You will not owe tax on your payment when you file your 2008
federal income tax return. But you should keep a copy of the IRS letter
you receive later this year listing the amount of your payment. You
will need to know this amount next year when you fill out your 2008
return.

Q. Will the payment I receive in 2008 reduce my 2008 refund or increase the amount I owe for 2008?

A. No, the stimulus payment will not reduce or increase your refund when you file your 2008 return.

So, that’s a little bit of good news for next year.  I guess it is more or less free money, except for all borrowing and interest the government will incur to provide us this windfall.  Personally, I think we are going to save this little bonus. Though, it would be fun to spend it 🙂