The GAO recently conducted a study on the use of social security numbers in public records. According to the study highlights:
Social Security numbers appear in any number of records exposed to public view almost everywhere in the nation, primarily at the state and local levels of government. State agencies in 41 states and the District of Columbia reported visible SSNs in at least one type of record and a few states have them in as many as 10 or more different records.
An InformationWeek article, Many Counties Put Social Security Numbers Online, offers additional commentary on the study.
Source: The E-LawLibrary Weblog