It's interesting -- how does Google actually measure quality? The naive approach would be to measure the number of clicks an ad attracts, as an initial indication of usefulness is how many people click. But that encourages ads that look like search results, frankly. Or ads for products people would have naturally found through organic searching. And Google's never point-blank asked me if I found an ad useful, though perhaps they could time how quickly I clicked another link from the same search result, and how often advertisers themselves keep paying for the same keywords.

Ultimately, ads need to make more money for a company than they cost to run. And my main issue is I'm being sold twice here -- first by being shown ads, and second by being featured in ads. This "double dipping" seems a bit much to me, so I opted out.