Today I saw a strange new Adsense unit on our blog. Our single posts feature a 336x280px Google adsense unit below the title, and instead of the usual 4 text links and descriptions aligned one below the other, the 4 text links were arranged in a 2×2 box pattern.
Filling up ad space using 2×2 ad units is common practice to get more clicks. Many webmasters used to place two 468x60px banner units one above the other or use two 200x200px units side by side to get the same effect of displaying 2×2 boxes of 4 ads together which is a good optimization of ad space. Probably Google is running a test run to see how these ads are clicked.
BTW those arrows are ‘next’ and ‘previous’ arrow buttons – When a user clicks on the ‘next’ button, an entirely new group of ads will appear in the ad unit, giving your users greater control over the ads they see and click.