The Joint Economic Committee has released Individuals and the Compliance Costs of Taxation.  Here is the abstract:

The federal tax code imposes a compliance burden of approximately $83 billion on individuals because of the time requirements of filing. This paper examines how people respond to these costs, given certain constraints. It is commonly believed that complexity: (1) reduces levels of voluntary compliance, either through avoidanceor evasion; (2) increases the difficulty in administering the tax law; and (3) may reduce the perceived level of fairness in the federal tax system.