Like Kleenex is to tissues, or Google is to search, so Facebook is to social networking. But the growth areas for social networks -- long the domain of teens and young adults -- has now shifted to an older crowd. EMarketer estimates that 105.8 million U.S. adults will visit social networks at least once a month this year -- about 59.2% of all adult Internet users. By 2014, nearly three-quarters (73.8%) of Internet users ages 35 to 44 and two-thirds (64.6%) of those ages 45 to 54 will be regular social network users. To find out more about digital marketing and eMarketer's report "Social Network Demographics and Usage," click here.