The Congressional Budget Office has released Did the 2008 Tax Rebates Stimulate Short-Term Growth?:

In preparing its economic forecast published in September 2008, CBO estimated that 40% of the tax rebates issued in the spring and summer under the Economic Stimulus Act of 2008 would be spent within six months––raising the growth of consumption in the second and third quarters of 2008 by 2.3% and 0.2%, respectively, and reducing it by 1.0% in the fourth quarter, when the distribution of the rebates was expected to end. However, analysts disagree about the economic impact of tax rebates. One study of the 2001 rebates suggests that as much as two-thirds of those rebates was spent within six months. For the 2008 rebates, some analysts have put the figure as low as 10%-20%––in contrast to CBO’s estimate of 40%. There is, however, disagreement among analysts about the economic impact of tax rebates. Today CBO released a brief that examines the issue in light of the evidence currently available.