WOMMA http://www.womma.org/blog/2008/10/marketing-messages-and-the-media-consumption-channel/

According to a joint research project by Ball State University’s Center for Media Design and e-mail service provider ExactTarget, consumers aged 18 to 34 report they are more likely to respond to an e-mail marketing message or direct mail than to one they get through a social channel. The study combined observed daily media use by 350 participants with data from the Channel Preference Surveys done by Indianapolis-based ExactTarget.