In April, Facebook users spent 13.9 billion minutes on the site, a dramatic hike from the year-earlier total of 1.7 billion minutes, according to a report from The Nielsen Co. The 700% increase let Facebook easily maintain its place atop the social networking business.

MySpace, according to Nielsen, came in a distant second place as users spent nearly 5 billion minutes on the site during April. The company fell far behind Facebook as its usage fell by 31% from April 2008, according to the Nielsen report.

Facebook cannot rest on its laurels as another hot social network, Twitter, grew even faster this year.

Though its only the fifth most popular social networking site, use of Twitter increased by 3,712% to nearly 300 million minutes.

"We have seen some major growth in Facebook during the past year, and a subsequent decline in MySpace," said Jon Gibs, vice president of Nielsen's online media and agency insights. "Twitter has come on the scene in an explosive way, perhaps changing the outlook for the entire space. The one thing that is clear about social networking is that regardless of how fast a site is growing or how big it is, it can quickly fall out of favor with consumers. Remember Friendster? Remember when MySpace was an unbeatable force? Neither Facebook nor Twitter are immune."

But while Twitter users are spending an increasing amount of time on the site, another Nielsen study out at the end of April showed that the microblogging site lacks loyalty among its base. That report concluded that some 60% of people using Twitter during one month, don't return to the site in subsequent months.

"Let there be no doubt: Twitter has grown exponentially in the past few months with no small thanks to celebrity exposure," wrote David Martin, vice president of Primary Research at Nielsen Online, in a blog post. "People are signing up in droves, and Twitter's unique audience is up over 100% in March. But despite the hockey-stick growth chart, Twitter faces an uphill battle in making sure these flocks of new users are enticed to return to the nest."