From Lawrence Lindsy via WSJ:
'The economics of what Sen. Obama is proposing should be at least as troubling. A high-income entrepreneur would see his or her federal marginal tax rate rise to 53% from 37.7% under Sen. Obama's tax plan. He proposes a 4.6 percentage point hike in the personal income tax rate, a loss of some itemized deductions, and a 12.4 percentage point hike in the Social Security payroll tax. This would take a successful entrepreneur's effective marginal tax rate higher than what it was under Jimmy Carter or Richard Nixon, when the maximum tax on an entrepreneur was 50%.
One of the lessons from the disastrous economics of the 1970s and the subsequent Reagan tax cuts is that everyone – particularly entrepreneurs – responds to incentives. If you take away 10% of a high earner's after-tax income at the margin, he will cut his taxable income by at least 4%. At the margin, this taxpayer now takes home 62.3% of his earnings, a figure that will drop to 47% under the Obama plan. According to a widely accepted economics rule of thumb, the entrepreneur's taxable profit would drop by 11.2%.'