Some more results, and I'm quoting from p. 44 of the report:
"Some 37% of internet users have actively contributed to the creation, commentary, or dissemination of news. We arrived at that figure by adding up the number of internet users who said they did any of the following activities:
• 25% of internet users have commented on an online news story or blog item about news that they read
• 17% of internet users have posted links and thoughts about news on a social networking site like Facebook. That translates into 30% of social network site users.
• 11% of internet users have tagged or categorized content online
• 9% of internet users have contributed their own article, opinion piece, picture, or video to an online news site
• 3% of internet users have used Twitter to post or re-Tweet a link to a news story or blog. That amounts to 18% of Twitter users."