A new feature on the Google News home page shows which stories have been shared the most by Google users and on Twitter, though it isn't clear if Google is tracking any other sources (e.g., Facebook). You have the option of viewing the most shared stories over the past 24 hours, past week, and past month.
This box appears at the bottom right of the main Google News page, so not in a very prominent position. Readers can click on the story, and also share the story themselves via e-mail, Google Reader, Facebook, Twitter, or Google Buzz.
Google hasn't made an official announcement, so it isn't clear if this is a test or permanent addition.
Last month, Google News tested a similar feature known simply as "Friends" to help Google users find news articles that friends shared on Twitter.