Yahoo, Microsoft, and AskJeeves are all homing in on the advertising niche that Google now dominates -- selling ads that are linked to search keywords, with the advertiser paying on the basis of clickthroughs.

There is indeed gold in them thar hills, because this kind of advertising is far different from advertising in most traditional media. To someone listening to music on a radio, advertising is an irritating interruption. Few people in the audience are interested in hearing Ronnie Mervis hawk his diamonds, and to all the rest his blathering is pure noise. The fundamental dilemma of the broadcast media is that the cost of reaching those few and selling them to Ronnie is the alienation of the rest. This is the dynamic behind the growth of satellite radio, which charges me about 2/3 of a cent NOT to listen to Ronnie, which is one of the best bargains in town.

But if I do a keyword search for "diamonds," the odds that I care about Ronnie go up incredibly. Maybe I am just doing a high school term paper, but maybe I am a buyer, and will regard a Mervis ad as agreeable information rather than irritant. And even for the term paper writer, the ad is off to the side, where it is an irrelevance rather than a positive negative.

In stock market commentary, one often sees the point that Google should be viewed as a media company rather than a part of the tech sector, but this is not quite right because the targeted ad model is so unlike anything we are used to that its economic and social characteristics are quire different.

The closest parallel in the pre-Internet world are specialized magazines -- those who buy Bride or Guns 'N Ammo or PC World are often as interested in the ads as in the articles. Or there is Lucky, the magazine devoted to shopping, which has no articles at all. But the immense costs of physical distribution render this model of dubious relevance to the Internet model.

Conventional broadcasting is likely to take a big hit, as people turn to the TiVo and its ilk, the iPod, and satellite radio, and battalions of techies are sweating at this very moment to try to figure out how to make broadcast advertising less offensive. For example, an interactive TiVo'ed program could run a five-second blurb telling you that information on the latest SUV is available if you want it, and not otherwise. For those who clicked, the ad would run; for everyone else, the program would resume. The advertiser would pay only for those who watched the whole ad.

But the medium with the worst problem is probably the newspapers. For decades, its mainstays have been ads for department stores, supermarket sales, and other mass merchandisers, plus the classifieds.

The papers do not have the problem that ads are irritants, unlike the broadcasters, because print ads do not demand one's time and attention. But, in any city - take Washington, for ex -- Hecht's department store, or the congressional aide with a bike to sell, have been stuck paying the Post's monopoly rents, plus the costs of physical distribution of a million copies of an ad that is regarded as useful information by only a few thousand, or even a few dozen, readers. A system whereby those few go on the Internet and type "bike" or "Hecht" is so incredibly more efficient that it is difficult to see how the ad-based newspaper can survive.

Furthermore, change is likely to be very fast. For the people who care, the Hecht's ad or the bike sale notice are indeed information and they are willing to buy the newspaper to get it. But precisely because they are active seekers of information, they will easily reprogram to look at the Internet. So the question on which the survival of the newspapers depends is, how much will Hecht's pay to reach those people who didn't know they were interested in a department store until they saw the ad? Something, but not as much as it pays now, by quite a bit. And the bike seller will pay nothing; for classifieds, there are no such people.

So yes, these are media companies, but not in any form in which media companies now exist, except maybe for the specialized magazines. And watching the unfolding of a logic that we can only dimly perceive at the moment is going to be fascinating.