I refuse to accept the view that mankind is so tragically bound to the starless midnight of racism and war that the bright daybreak of peace and brotherhood can never become a reality. - MLK
Based on the 2011 tax tables the top rate of 35% starts at 379,150. Without taking anything else into account (deductions, exemptions, credits, etc...) if you made 500,000 in salary you would owe 152,314 at the 35% rate. If the top rate was raised to 38% you would end up owing 155,939.50. For an increase of 3,625.50. This is a .7 percentage point increase in your effective tax rate, from 30.5% to 31.2%.
Of course as you make more money the impact is greater because more of your money is taxed at the higher rate. So if you made a million dollars your taxes would be 18,625.50 higher at the higher rate. In this case your effective rate goes up 1.9 percentage points, from 32.7% to 34.6%.