In the early days of both radio and TV, commercials were always done live - and integrated into the show itself. TV execs have been toying with various ways to defeat DVR and Tivo zapping (the techie word for fast forwarding through breaks) since advertisers feel they aren't reaching their audiences and started moving ad dollars to other mediums, like the Internet.
During the days of The Tonight Show with Johnny Carson, Ed McMahon did live commercials on a regular basis, with the last airing in 1995.
Well Tuesday Night 6/12, The Tonight Show with Jay Leno is bringing back that tradition with a live commercial to be done by booth announcer John Melendez for the satellite navigation system Garmin International.
According to the Wall Street Journal, the spot will be played out right before the second regular commercial break during the show.
NBC is experimenting with the concept and, if successful, will likely be used in the future.