So simple it hurts, from Yahoo by way of the New York Times.
The gist? The seemingly simple ability to remember the higher-value pages a user views lets you serve that user those higher-value ads on all pages. Tada!
So travel pages often fetch the highest rates from advertisers. Let’s say a user checks out some travel articles about Nicaragua and surfing, where you serve some awesome ad from some awesome hotel chain. Then the user reads about President Obama. It turns out—by virtue of the great good blessings of technology—that you can still serve the same awesome hotel ad, not some barrel-bottom trash, even though, all else equal, advertisers don’t care so much for the attention of users who care about civics.
Who knew, right?