More than half the country actively uses social-networking sites, but so far advertising on these properties is nothing short of anemic, says a new report issued by market research firm IDC. In fact, IDC calls advertisers’ attempts to tap into these sites’ unique social nature “stillborn.”

According to IDC’s report (U.S. Consumer Online Attitudes Survey Results Part III), more than three quarters of social-networking site users log on at least once a week, and 57 percent do so daily. And these folks are logging an increasingly large amount of time on these properties, as more than 61 percent of users spend more than a half hour on these sites per session, with 38 percent staying at least an hour.

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