According to another techcrunch article about a third of zynga's revenues are from these types of promotions. That being said - not all of them are of the scam

According to another techcrunch article about a third of zynga's revenues are from these types of promotions. That being said - not all of them are of the scam variety so while Zynga may take a slight hit they should be fine. Noting as well that this is a better long term position considering the social networks themselves would likely start policing these moves at some point.