While two-thirds of online American adults are Facebook users, most of them often take a break from the site for several weeks or more, a survey indicates. A poll by Pew Research Center\'s Internet & American Life Project also found 20 percent of online adults who do not currently use Facebook say they once used the site but no longer do so. Users gave many reasons for taking a break from Facebook either permanently or temporarily, including being too busy with other demands, a general lack of time, lack of interest in the site, a lack of compelling content, or excessive gossip or \"drama\" from their Facebook friends. However, even as many Facebook users adjust or cut back on their use of the site, the vast majority of social networking site users -- 92 percent -- maintain a profile on Facebook, making it the dominant social networking site in the country, a Pew release reported Tuesday. Still, some 42 percent of Facebook users ages 18-29 and 34 percent of ages 30-49 say the time they spend on Facebook on a typical day has decreased over the last year, Pew said. Pew conducted the telephone poll Dec. 13-16, with a margin of error of plus or minus 3.6 percentage points.