The Center on Budget and Policy Priorities today released New Analysis Shows "Tax Expenditures" Overall Are Costly and Regressive; Findings Highlight Need to Restrain Tax Subsidies As Part of Solution to Long-Term Budget Problems, by Chye-Ching Huang & Hannah Shaw.  Here is the abstract:

"Tax expenditures" — tax breaks that favor particular activities — for individuals totaled about $760.5 billion in 2007, topping what the federal government spent on either national defense or all non-defense discretionary programs. In most cases, they are also regressive. In light of their high cost and regressive nature, tax expenditures should be on the table when efforts to address the nation's long-term budget problems are mounted.

Exempting tax expenditures from fiscal discipline also would be inequitable. As the TPC analysis shows, tax expenditures deliver their largest benefits to upper-income families. In contrast, Social Security and Medicare benefits are spread far more evenly across the population. Protecting tax expenditures while imposing significant cuts on other parts of the budget would likely favor the well-off at the expense of the broad majority of Americans. It also would necessitate even deeper reductions in other parts of the budget than would otherwise be needed to restore fiscal stability.