Thus far this season, O'Brien's Tonight Show has trailed The Late Show with David Letterman by an average of 1.7 million total viewers, or 65%. (For comparison's sake, Leno had a 20% lead over Letterman's show last year.) Among the advertiser-beloved demographic of 18- to 49-year-olds, O'Brien and Letterman have fared about the same--not bad, until you consider that Leno had a 15% lead in that key area.

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In the years since, his broadcast network has continued to languish in the ratings basement, shedding another 16% of the advertiser-beloved 18- to 49-year-old demographic for the TV year ending in September.

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In fact, the Tiffany network rounded out another television season no. 1 in total viewers, a title it has held for seven of the last eight seasons. (For the advertiser-beloved 18-to-49-year-old demo, it ranks second behind Fox.) What its offerings lack in pop-cultural prominence they make up for in viewer loyalty.

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At the same time, Fox, which rounded out the first half of the season tied with NBC at No. 2 among advertiser-coveted 18 to 49-year-olds, is poised to blow past it now that American Idol is back on the air.

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