Earlier this month Australia's Advertising Standards Bureau (ASB) ruled that "an advertiser’s Facebook site is a marketing communication tool and therefore falls under the industry’s self-regulatory code of ethics" and that “the Code applies to the content generated by the page creator as well as material or comments posted by users or friends.” [emphasis added]
The ASB's ruling came about after examining the Facebook tactics employed by two large alcohol brands, Smirnoff and Victoria Bitter. In the case of Victoria Bitter, the ASB ruled that user comments on the Victoria Bitter Facebook page are subject to the same regulations as any other brand-generated advertising and as such must not glorify alcohol consumption in excess or express discriminatory or derogatroy sentiments.
Next, the ASB ruled that hundreds of event photos posted to Facebook by Smirnoff, a title sponsor for numerous concerts and music festivals, constituted micro-advertisements once they were disseminated thoughout users' social graph via likes, comments and photo tagging. As a result, such photos are bound by the same regulations prohibiting the depiction of excessive drinking culture and alcohol consumption by adults not clearly older than age 25.
It will be interesting to see if other countries adopt similar legislation using the same interpretations of what exactly consitutes "advertising" these days. You can read more about the ASB rulings here.