The IRS's Statistics of Income Division has released: Individual Income Tax Returns, 2007 (Publication 1304, Statistics of Income—2007):

The publication includes sections on changes in law, explanation of terms, and the description of the sample, as well as many statistical tabulations. Tables from Publication 1304 are also available and present data for the number of returns filed, sources of income, exemptions, itemized deductions, and tax computations. Data in the tables are presented by size of adjusted gross income, marital status, age, type of tax computation, and rate at which tax was computed.