Via hypergene mediablog, a report from the Pew Internet and Everyday Life Project:

44% of Internet users have created content for the online world through building or posting to Web sites, creating blogs, and sharing files.

• 21% of Internet users say they have posted photographs to Web sites.
• 20% say they have allowed others to download music or video files from their computers.
• 17% have posted written material on Web sites.
• 13% maintain their own Web sites.
• 10% have posted comments to an online newsgroup. A small fraction of them have posted files to a newsgroup such as video, audio, or photo files.
• 8% have contributed material to Web sites run by their businesses.
• 7% have contributed material to Web sites run by organizations to which they belong such as church or professional groups.
• 7% have Web cams running on their computers that allow other Internet users to see live pictures of them and their surroundings.
• 6% have posted artwork on Web sites.
• 5% have contributed audio files to Web sites.
• 4% have contributed material to Web sites created for their families.
• 3% have contributed video files to Web sites.
• 2% maintain Web diaries or Web blogs