In 1988, Congress banned video stores from disclosing the titles of films that people rent. The issue arose because in the battle to block Robert Bork from the Supreme Court, someone leaked his video rentals.

Fast-forward to this summer, and a federal judge hearing a $1 billion copyright complaint by Viacom ordered YouTube to turn over online records about which computer addresses were used to watch which videos on the site. The judge dismissed privacy concerns as "speculative." How quickly our expectations of privacy have...