The Government Accountability Office has released Puerto Rico: Fiscal Relations with the Federal Government and Economic Trends during the Phaseout of the Possessions Tax Credit (GAO-06-541) (225 pages):

This report provides information on the Puerto Rican economy, including corporate activity, during the phaseout of the possessions tax credit, as well as descriptions of the application of federal tax law and federal social policy programs in Puerto Rico.

The Joint Comittee on Taxation has released An Overview of the Special Tax Rules Related to Puerto Rico and an Analysis of the Tax and Economic Policy Implications of Recent Legislative Options (JCX-24-06) (120 pages):

This pamphlet, prepared by the staff of the Joint Committee on Taxation, provides an overview of the special tax rules related to Puerto Rico and an analysis of the tax and economic policy implications of recent legislative options….Part I of the document provides an executive summary of the pamphlet. Part II discusses the present law tax provisions related to Puerto Rico and other U.S. possessions. Part III covers the mechanics of the possession tax credit. Part IV traces the legislative history of the possession tax credit and summarizes the findings included in several government reports released over the last 20 years. Part V contains an economic analysis of U.S. Federal tax policy issues relating to economic development in Puerto Rico. Part VI is a description of the Puerto Rico statehood, commonwealth and independent party agendas. Part VII is an analysis of the tax and economic policy implications of recent proposals regarding the U.S. tax treatment of Puerto Rico.