There's advantages to showing advertisements recommended by a person's friends, says Nielsen in a study of 79 Facebook campaigns over a six month period.

Social ads are defined as:

... those served to users who have friends that are fans of or have interacted with the advertised brand and prominently call the relationship out, while non-social ads are served to the remainder of the Facebook population.

Ads with Friends: Analyzing the Benefits of Social Ads | Nielsen Wire

The research shows that social ads are recalled by a margin of 55% over non-social ads.

Foremski's Take: Ad recall is not the same as conversions. For example, advertising on social networks such as Facebook, has a far lower click through rate than online advertising on non-social sites.