According to the description from "Google in your Language", the message is used for "an ad that is determined to be particularly likely to be useful or relevant for a user".
I wonder if the new feature is related to Google's interest-based ads, which "associate categories of interest — say sports, gardening, cars, pets — with your browser, based on the types of sites you visit and the pages you view. [Google] may then use those interest categories to show you more relevant text and display ads."
{ The first screenshot is licensed as Creative Commons. }