The implications of a shutdown of the federal government due to funding gaps are discussed in a newly updated report (pdf) from the Congressional Research Service.
“Failure of the President and Congress to reach agreement on interim or full-year funding measures occasionally has caused government shutdowns, the longest of which lasted 21 days, from December 16, 1995, to January 6, 1996. Government shutdowns have necessitated furloughs of several hundred thousand federal employees, required cessation or reduction of many government activities, and affected numerous sectors of the economy.”
See “Shutdown of the Federal Government: Causes, Processes, and Effects,” February 18, 2011.
See also, relatedly, this CRS report on “Reaching the Debt Limit: Background and Potential Effects on Government Operations,” February 11, 2011.