From the Wall Street Journal
The tax increases would ... [reduce] the value of such longstanding deductions as mortgage interest ... for people in the highest tax brackets. Households paying income taxes at the 33% and 35% rates can currently claim deductions at those rates. Under the Obama proposal, they could deduct only 28% of the value of those payments.
The changes would be phased in gradually over the next few years. For the 2009 tax year, the 33% tax bracket starts with couples with taxable earnings of $208,850, when adjusted for personal exemptions and various deductible expenses. A taxpayer in the top bracket paying $1,000 of mortgage interest, for example, would see a tax break worth $350 reduced to $280.
The mortgage interest deduction is capped to $1 million in mortgage debt.