Only the income above the tax bracket is taxed at the higher rate, not the entire income. For example, you make $100,000 in 2009 and you are taxed at 25% and you would pay $25,000 in taxes. The tax bracket above $100,000 is 32% and you make $100,010 in 2010. Your tax for 2010 would be 25% of $100,000 and 32% of ten dollars. So your new tax would move from $25,000 to $25,003, not $32,000.
This is the concept of marginal tax rates. Also, this is only an example, please do not use these numbers for income planning purposes. You should seek the advice of a qualified tax professional, which of course usually excludes most posters on SDN.