A new Forrester Research study indicates that social networking sites in the U.S. have now gone mainstream, according to AdWeek.

The numbers are pretty startling: A consumer poll from the second quarter of this year showed that 75 percent of Internet users participate in some form of social media, which is up from 56 percent one year ago in the same period.

Content creation growth has slowed, however, according to the report. "Those publishing a blog or personal Web page saw incremental growth: 21 percent versus 18 percent. In fact, blogging grew just 10 percent, well behind the 39 percent growth in starting a social network profile." In general, 48 percent of respondents said they've read a blog, which is almost a 50 percent increase from last year.

"The novelty of today's social technologies will eventually wear off, and consumer adoption will plateau as all new media eventually do," Forrester analyst Josh Bernoff wrote.

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