facebook, twitter, pinterest, social networks, social mediaTwo-thirds of adult Americans online use Facebook, but just 8 percent of non-users are interested in joining the social network, while 61 percent of current users have at some point walked away from the site for a period of several weeks or more, according to a Pew Internet study.

The numbers suggest that Facebook faces an uphill battle in retaining its user base in the United States. While more than half of the users polled said they spent as much time on Facebook in 2012 as they did in 2011, more than a third said their usage had fallen off. Just 13 percent said they spent more time on the site.

One in five online adults who doesn’t use Facebook is a former user.

Users who had left the social network temporarily or permanently cited boredom and privacy concerns as causes of their dissatisfaction.

Among those who took a break from Facebook, lack of interest in the site, absence of compelling content, excess of gossip or “drama,” and interference with their productivity each accounted for about 10 percent. One in five of the users who took a hiatus said they were simply too busy.

“I didn’t like being monitored” and “I don’t like their privacy policy” were also among the explanations users offered.

Irritation with the “gossipy” nature of the network and dissatisfaction with its privacy policy also drove most of the former users away.