The Wall Street Journal has an editorial about the proposal by Senate Democrats to impose a 5.6% income tax surcharge for ten years on taxpayers earning $1 million a year or more beginning January 1, 2012. The editorialists wonder: "How this would stimulate a sluggish economy even under Keynesian economic theory is a mystery, unless you believe like Democrats apparently do that tax rates don't matter to economic growth."
I agree with the Journal that this tax is a bad idea. But it's not entirely mysterious to see a theory under which it would have some short term positive economic effects. Investment bankers and merchant bankers would see a boom in fees as business owners rushed to sell businesses and structure deals in such as way as either to recognize the income in 2011, before taxes increase, or to spread the income out over longer time periods so that the surcharge does not apply. You might get some additional effects in terms of spending on luxury goods like cars or boats or real estate as wealth that was once tied up in company stock all of a sudden is more liquid. The Congressional Budget Office scores capital gains tax increases as positive for government revenue the year before they go into effect, and negative the year after they go into effect, because of the income-shifting effect as individuals choose when to realize their gains. This 5.6% surcharge, at least as I understand it, would also apply to capital gains income. So it would have effects similar to a capital gains increase. It would stimulate the economy between now and the moment it goes into effect.