The Google AdSense Blog announced they have made the “biggest performance overhaul” to the AdSense link units in history.
This update was a “full rewrite of the link unit matching system,” which is pretty significant. Google tells us we can expect the link units to return better ads. The ad system uses a “more sophisticated topic ranking algorithms” and continues to improve the link units by “learning which topics have the most appeal to the visitors.”
Ultimately, Google hopes this leads to better quality ads, which drives more clicks and more money.