No big secret here about the proposed tax scale. He has a tax calculator right at his website:
http://taxcut.barackobama.com/
My understanding is that tax cuts will go to families making under $150k per year, those making between $150k and $250k per year will have no change in their taxes, and those making over $250k per year will have a 3.6% increase in only their income above $250k.
So if you earn $350k, you will pay 3.6% more on $100k of your income.