The ad unit, which will be announced this week at Advertising Week in New York, is subtly different from Sponsored Stories, which rolled out in January, in two ways: it won't ever appear in the News Feed and -- unlike Sponsored Stories, which merely show an interaction with a brand -- it also contains an advertiser message. It's also different from Social Ads, which tell you if a friend took an action related to the brand.
Instead, the new ad unit will expand to let you comment and see other comments related to the ad. This mock-up ad for The Ides of March (no advertisers have signed on yet) shows a "like" from the user as well as the copy:
The ad unit is based on the belief that ads with recommendations from friends will be more effective than standard display ads and magnify a brand's reach. For instance, research Facebook undertook in May with comScore found that Starbucks fans and friends of fans spent 8% more at the coffee chain than other Internet users.