I've written in this space before about how I think the Unifying Theory of Advertising doesn't work on the Internet. There are too many ways in which a user can ignore or outright disable ads. This cuts down on the number of people who view the ads, and in turn, how many people buy the stuff featured in the ads.

Read/Write Web today takes issue with the advertising technology at the heart of Facebook's potential $15 billion valuation (based on Microsoft paying $240 million for a 1.6% stake).

The problem, writes Alex Iskold, is that "people are not coming to Facebook to click ads." Ignoring for a moment the other half of Iskold's thesis -- that Facebook isn't capable of delivering relevant ads that people want to click on -- we're left with a problem that could bring down Web 2.0.

I've said it before: people don't like advertising. They tolerate because they have to, and whenever they can easily get around it, they do. Advertising is reaching a saturation point, and it won't be long before people, fed up with constantly being marketed at, abandon forums that contain advertising in favor of forums that don't. If Facebook becomes too ad-oriented, it runs the risk of alienating its users at worst, and losing revenue from users who don't buy the products advertised. Once the revenue goes down, then ad-based social networking sites -- which are most of them -- will find themselves in the unemployment line right behind Web 1.0.