Liesbeth, Passive use may be widespread, at least on some sites. In a study of online video sites, Cha et.al. found that users rated the video on only 0.22% of YouTube views, and commented on 0.16%. They cite a Reuters article that reports that Hitwise have found similar results: only .16% of visits to YouTube are video uploads, and .2% of Flickr visits are uploads. I have not been able to get my hands on any publication from Hitwise. Is this special for YouTube, Flickr, and other sites that the OfCom study named "User Generated Content sites" (and were not regarded social network sites), or can we expect similar numbers for Twitter, Facebook, etc.? Cha, Meeyoung, et al. "I Tube, You Tube, Everybody Tubes: Analyzing the World's Largest User Generated Content Video System." Proceedings from the Internet Measuremet Conference, San Diego, 2007. New York: ACM, 2007. <http://portal.acm.org/citation.cfm?doid=1298306.1298309> Auchard, Eric. "Participation on Web 2.0 Sites Remain Weak". _Reuters.com_, 17. April, 2007. <http://www.reuters.com/article/internetNews/idUSN1743638820070418
--anders