Joel Spolsky writes:
With Google rapidly approaching 50% of the global search market, they can double the number of searches they get on their home page, but not much more than that, unless they can get more page views somehow. Which is why they are frantically trying to sign up non-fraudulent web sites for AdSense (they call me every two months) and constantly seeking new sources of ad inventory, which sounds a heck of a lot like what the web portals of the 90s tried to do.
This is where Google is actually hurt by the long tail world of millions of small sites. It’s easy to evaluate the top 100 or 1000 web sites to make sure they’re reasonably legit. It’s much harder to monitor 1,000,000 blogs to make sure that none of them were machine generated for the purpose of scamming AdSense revenue. Still, I don’t think Google has a choice: I predict that you’ll see a massive expulsion of smaller AdSense sites by Google, and it better happen soon, or AdSense will ruin Google’s reputation among advertisers, something which could be deadly.