Earlier this month, we reported that AdSense was testing new arrow formats in their ad units. I personally didn't see it, but it seemed like others were seeing various tests.
Google has finally confirmed the tests in a blog post that says we should notice new types of arrows that are more visible. The blog post said:
We've been testing slight updates to the look of these arrows, and our experiments have shown improvements in the user experience. As a result, we'll soon be making a few minor aesthetic changes, including darkening the arrows to make them more visible and orienting all arrows to point left and right. In addition, to help users understand what the arrows do, hovering over the arrows will soon show the labels 'previous ads' and 'next ads'. You'll see these changes appear in CPC ad units in all languages gradually over the next few days.
I now see the difference on my personal blog.
Old Arrows from June 2008:
Small but noticeable difference.
Forum discussion at Google AdSense Help.