We'd like to officially welcome you to The Facebook Age. Now, according to a new report from Forrester Research, more than four in five U.S. online adults report using social media at least once a month, while half report participating in social networks like Facebook.

And while young people continue to march toward almost universal adoption of social applications, the most rapid growth occurred among consumers 35 and older.

"This means the time to build social marketing applications is now," said Forrester analyst and report author Sean Corcoran. "Interactive marketers should influence social network chatter, master social communication, and develop social assets -- even if their customers are older."

Forrester's analysis of the Social Technographics Profile of online Americans over the past three years shows that "joiners" -- the group that uses social networks -- had the most explosive growth.

Nearly one-quarter of U.S. online adults are new "creators" -- people who write blogs, upload original audio or video, or post stories online. "Easy-to-use blogging tools encouraged some less tech-savvy adults to create social content this year, but the majority of consumers are still consuming, not creating, content," said Corcoran. The critic group, meanwhile, did not grow in 2009. While more than one-third of online Americans still take part in activities like posting reviews and commenting on blogs, fewer now contribute to online forums. Why?

"We think consumers shifted their discussions to major social networks like Facebook," Corcoran said.

Collectors, those who organize online content, grew slightly. One in five online adults categorize Web content via tags, RSS feeds, and "voting" sites like Digg and Reddit. Consumers' rapid adoption of applications that use tags, like Facebook and Twitter, boosted this group's growth.

Joiners swelled to one in two online adults. Half of online adults now belong to social networks like Facebook and LinkedIn, a 46% growth rate year-over-year.

Both friends' encouragement and press coverage likely drew people to these sites, according to Forrester.

Nearly everyone's a "spectator" as three in four online Americans now consume social content, while user-generated video viewing, blogs, and online reviews drove the growth of social content consumption.

Inactives now represent less than one-fifth of online adults, as only 18% of U.S. online adults don't use social tools in 2009 -- down from 25% in 2008.

Who participates socially? "Everyone," according to Forrester's research. "Adults of all ages increased their use of social tools." Adults younger than 35 approached universal social participation, while adults ages 18 to 24 and those ages 25 to 34 adopt social media similarly. Only 3% of 18- to-24-year-olds and 10% of 25- to-34-year-olds are socially inactive.

What's more, a staggering 89% of the younger crowd are spectators, while nearly as many are joiners. And almost half create content -- far higher than any other age group. Adults ages 25 to 34 also grew their participation across all categories -- especially in social networks. The message here: Social applications are necessary in every marketing plan that targets young adults.

Forrester encourages marketers to develop social applications, even if their audience is mature. "Social media can no longer be dismissed as a quirky habit of young adults," Corcoran said. "Nearly all online adults now participate socially, including those in their 40s and 50s."

Forrester further recommends crafting a brand's social entrance quickly, as "hesitating will force you to chase competitors who've already launched their social strategies."

To garner its insights, Forrester conducted the North American Technographics Interactive Marketing Online Survey in May 2009, which surveyed 4,766 U.S. individuals ages 18 to 88.

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