If this stat meant anything, Yahoo’s ad network would be worth 93% as much as AOL’s, Google’s 89% of AOL’s, and ValueClick’s 82%. But of course, that’s not the case.

In Q4 of 2007, Google paid out $1.3 billion to its AdSense partners, Yahoo paid out about $430 million, and AOL paid out about $250 million. I’m basing this on company-reported TAC, or traffic acquisition costs, which is what they call revenues shared with network partners.

Of course, the companies all use their own networks, too, and take varying fees. But for an apples-to-apples comparison of market force or industry power — if not value — TAC comparisons are useful. (ValueClick’s total revenues were $183 million in Q4.)

Fellow members of the digerati and commentariat, please stop obsessing about absolute reach. Without more context, it’s a worthless metric.