Well, according to this Washington Post piece, predictable enough that candidates no longer need to actually pay for advertising time. They take their most controversial ads, show them to the press, and the press (especially the talking heads on cable) blather about them incessantly. Instead, the candidates actually run much more centrist ads in the major markets. Also, broadcasters have reported that, contrary to expectation, campaign advertising has not proven to be a "bonanza." Outlets in contested states are certainly doing well, but not as well as they had hoped given the overall decline in business advertising.