Brafton reported that Facebook was using the conversations of users' friends to promote products with Sponsored Stories. Now, it seems the social giant is testing a similar ad service that promotes products based on real-time Facebook activity.

Though there is no official word from Facebook, some users are seeing a new ad format that displays advertisements related to their Facebook updates and wall posts. AdAge broke news about the testing of the ad unit this week. It seems some of the ads delivered are for general brands, while others are for businesses located near users.

In an age where relevancy and location are proving key to reaching online consumers, this ad format may hold promise for marketers who want to reach the right Facebook audience.

“The long-held promise of local is to deliver timely, relevant and measurable ads which drive actions such as commerce, so if Facebook is moving in this direction, it's brilliant,” AdAge quotes Reggie Bradford, CEO of Facebook software and marketing company Vitrue, as saying.

At the same time, this ad unit might disturb some Facebook users who feel the site is too closely monitoring their activity. As Facebook continuously faces privacy issues, this is a potentially widespread concern.

The new ad may be controversial, but business can still reach out to Facebook users and build their fan bases with original, branded content – and data from L2 ThinkTank indicates that Facebook fans are a valuable audience.

Mashable quotes Scott Galloway of L2 ThinkTank as saying, “Forty percent of Facebook users follow a brand, and 15 percent of those fans intend to make a purchase from that brand within 60 days.”