Basically, there is a idea of privacy through difficulty of access that digital records violates. Many records, including real-estate purchase documentation, have been matters of “public record” for at least fifty years, but were only available if you were willing to go to a moldy records archive in some county office and dig through mountains of boxes of files. (If they were not already, they were made public as a part of Civil Rights laws)

This was difficult and time consuming, raising a sufficient barrier to entry for the average person.

Recently, those same records are being digitized, and are available at no cost online. In badly run databases (such as the one the campaign finance information is in) this is fine – access is still sufficiently difficult. However, the newest innovation is mining that data into things like this mashup.

A hot policy issue is — for the first time in American history — reducing access to public documents, especially when they may contain sensitive information that “should” not be placed online.

Other examples:
http://zabbasearch.com/ – a database which, for free, provides the home phone number, address, and birthday for almost anyone who has ever owned a home. Very creepy – includes unlisted numbers and other “private” information.

http://www.mapsexoffenders.com/ – Google mashup of sex offender registrations. May have beneficial uses, but has caused several documented instances of violence.