Google has made subtle yet important changes to how AdWords ads appear above search results, it announced on the official Inside AdWords blog.
The first, and relatively minor, change is that the color on those ads has shifted from blue to yellow. The second change has more of an impact on actual ad performance.

Instead of having any click within the shaded area of the box take users to the advertiser's website, the click must now be directly on the link.

The Inside AdWords blog hints, and Marketing Pilgrim guesses, that this change is being made because too many inadverant clicks were being made.

By limiting valid clicks to just the link itself, marketers aren't charged for accidental clicks.