More and more people  -- especially older people – are spending an increasing amount of time social networking, says a new report.

Nearly a third of the time Americans spend online is spent on Facebook and FarmVille, while time spent on traditional e-mail and portals such as Yahoo has dipped, according to a report by Nielsen Online released Sunday. (The decline in e-mail time is because more people are staying in touch by – you guessed it – Facebook.)

David Martin, Nielsen's vice president of primary research, told the San Jose Mercury News: "A platform like Facebook incorporates e-mail and instant messaging. Social networks have incorporated those basic functions in a much larger system of communication, content management and even gaming. The growth has come at the expense of traditional portals, e-mail platforms and IM."

The report – called "What Americans Do Online" – also revealed that twice as many Americans over 50 visited social networks than kids under 18.

The study followed 200,000 fixed Internet PC users in June 2010, and compared it to June 2009.

It revealed that Americans spend about 24 hours per month online using desktop computers. (The study didn't include, for example, how people reaching the Internet on their cellphones spend their time. A separate study, from the Pew Research Center, revealed that 38 percent of mobile users get online via their phones, compared to 25 percent a year ago.)  

According to the Nielsen report, the top way to spend time online is on social networking sites, which vacuumed up 23 percent of people's time. That's up from 16 percent a year ago. No. 2 on the time-spent list is online games such as Zynga's FarmVille. (Half of all Americans spend some time online playing games.) Total percent of Internet time for social networks and online games: 32.9 (up from 25.1 percent last year). E-mail sank to No. 3 on the list, occupying 8 percent of people's time online, down from 11.5 percent in 2009.

Besides social networking and game-playing, one other online activity is taking up more and more of people's time: Watching videos and movies on sites such as YouTube, Netflix and Hulu. Streaming increased 12 percent, with American Internet users spending about 3 hours and 15 minutes per month watching online videos.

Of the social networking sites, Facebook – which last month hit 500 million users – ran away with the popularity contest crown. Nearly 85 percent of all time spent in the sector is on Facebook, compared to just 5.6 percent for MySpace, the runner-up. Twitter and Blogger tied for third place, with 1.1. percent. (Keep in mind, of course, that lots of users access Twitter through applications other than – one reason that the microblogging site wasn't included in the recent American Consumer Satisfaction Index.)