Wouldn't have guessed this -- since link units require an extra click.

Quoted: Recently, Julie experimented with optimizing her link unit ad placement. She removed the existing 120x90 link unit from the uppermost right corner of her pages, and instead placed a 468x15 link unit at the top of her articles. In doing so, Julie found a convenient, unobtrusive location and saw her readers naturally gravitating towards the link unit. Her efforts led to an immediate doubling of her revenue -- an increase that has been sustained since the move.

Cool. I wonder if Google AdSense for mobile is close behind?

Quoted: RCR Wireless News reports that Google AdWords customers in the US can now place marketing messages, including linked text, in results from Google’s mobile search service. A similar service has been available for over four months in Japan

Quoted: CPC is, and will remain, the most cost-effective, affordable and balanced ad model for both advertiser and publisher. If its underlying problems can be addressed (click fraud, etc.), CPC can provide a radical improvement to overall ad performance and result in sustained productivity growth. Also, increases in productivity - which we've seen a lot of in recent years - is what most drives economic growth without causing inflation.

More from Seth Godin on AdSense.

Quoted: So, Google AdSense ads across the top increase confidence. They’re recognizable and safe for the surfer. They make it clear that there are alternatives. They demonstrate confidence on the part of the site builder. Analogy: All car dealers do better when they’re on the same street.

Quoted: Google is adding another way of generating revenue -- in the works is a new advertising network that will complement its current fraud-prone AdSense network.