…at least for a couple of months.

The general rule for SSI financial eligibility is that an item of income received, is "income in the month received, and becomes a resource (asset) on the first of the following month" if still retained by the disabled or elderly SSI recipient.

However, EM-08029, an Emergency Message to SSA staff, declares that checks received as part of the Economic Stimulus program will not count as income in the month received, and will NOT become a resource for two months more:

 Income

Any payment made to any individual based on this law will not be counted as income for purposes of determining eligibility and payment amount for SSI.

Resources

If the payment is retained by the individual, it will not be counted as a resource for 2 months following the month of receipt. For example, if the individual receives a payment in May 2008, it will be excluded from resources for June 2008 and July 2008. In this example the funds, if retained, would be countable as a resource starting in August 2008.

I doubt poor people will have to wait two months to spend that $600 check.  It’ll be gone in a jiffy paying for that $4.50 per gallon Texas gasoline!