Adsense and the advertising/editorial wall
You are probably familiar with Google adsense, which is providing the ads you see on the right hand side of this page. Adsense code examines the text of pages, and tries to match Google adwords bids against it. The publisher of the page gets some undisclosed share of the Google revenue.
Recently adsense has been improving a lot for me, and my revenue from it per day has more than doubled, either due to better ad placement, better share or higher bids -- it's hard to say. It has gotten good enough that one can now readily see making a living as a good web writer through adsense. At an extreme example, my Copyright Myths article, which is admittedly very popular, is now generating over $250 per month in revenue. Just that one article. An author able to generate articles that popular (admittedly difficult, part of the popularity comes from having been around for decades and being linked to from many places) could make a living wage.
On one hand, Adsense seems like a great implementation of the wall that is supposed to exist between advertising and editorial. I have no idea what ads will appear, I don't control it. I have no relationship with the advertisers, and there are so many advertisers that it would be hard for any one of them to hold sway over me as a writer.
However, there is an opposite factor. Clearly some topics are much more lucrative than others. My jokes and photos pay just a small fraction of what writing on copyright pays, because there are lots of copyright lawyers willing to bid high to advertise to people curious about that topic. My spam essays pay decently because of anti-spam companies. My DNS essays get little traffic, but when they do they get people selling domain names etc.
In the extreme, if you become the big expert on a disease like mesothelioma, the asbestos caused disorder, laywers hoping to sign up clients will pay many dollars for every click. (It was famously the most expensive word in a survey last year.)
So there is a strong push now, for a writer wanting to make a living (instead of one like me getting some extra change) to write about the very specific topics that get high adwords or overture bids.
Part of this is nothing new. In the past the way to make the most profitable magazine was to cover a topic that would attract readers that advertisers want to reach. Some general media, like newspapers, sought only to gain an audience, and advertisers would pay to reach the general audience.
But advertisers don't want to reach a general audience, or only rarely do they wish to do so. Google has broken one of the great aphorisms of advertising, "90% of all advertising is wasted, the problem is figuring which 90%." And from this they have a multi-billion dollar business. But how will this affect editorial down the road?