Social-networking sites in general saw an increase in visitors, claiming 6.13 percent of U.S. Internet traffic, up four percent year over year, according to tracking company Hitwise. Facebook's share of that traffic more than doubled, to 36 percent from 14 percent.

"I think what is really interesting about the growth is how Facebook has continued to grow and Web-site traffic to Facebook has had an upright trajectory," said Heather Dougherty, director of research at Hitwise.

Demographics Are Changing

Moms aren't spending their nights out talking about their children spending time on Facebook -- they are talking about their own experience on the Web site. Tracking results show the site is not only attracting teens, but visitors aged 35 and older, a group that grew 23 percent from February 2008 through last month.

The older demographic may also be switching from MySpace to Facebook, since MySpace saw a two percent decline in that age group during the same time.

"When you look at the ages of visitors on Facebook, the biggest share is still aged 18 to 24," Dougherty said. In fact, 29 percent of traffic to Facebook last month was from that age group, 17 percent were 45 to 54, and nine percent were 55 and older.

Still, there is a clear shift away from Facebook being visited by just the 18-to-24 group. Traffic from all age groups -- except the 18-to-24 category -- increased from February 2008 to February 2009, according to Dougherty.

"It has become far more mainstreamed than it has in the past," she said. "You have parents going online partly to see what kids are doing, but certainly doing the same things others are doing by connecting with friends and colleagues. You have that network effect."

Gaining on MySpace

Once on Facebook, users are spending more time on the site. From February 2008 to last month, visitors six percent more time.

Some Internet users are spending so much time on Facebook that employers are reporting less productivity, and one priest said college students are giving up Facebook for the 40 days of Lent because it they see it as a huge sacrifice.

Facebook may be increasing in visibility and traffic, but MySpace, the older social-networking site on the block, is still at the top, according to Hitwise. But that may not be true for long.

MySpace's share of U.S. visits to social-networking sites was a whopping 52.21 percent, making it number one and beating out 55 other sites. That ranking, however, does not reflect MySpace's 28 percent decrease from February 2008 to last month.

"In February 2008, MySpace represented 73 percent of traffic, and in 2009 they had 52 percent," Dougherty said. "Looking at the data , you can see how it is possible that Facebook could pass MySpace in traffic to the site in the next months."

Facebook spokesperson Elizabeth Linder wouldn't comment on the figures, saying, "As a matter of company policy, we do not comment on third-party data."