Perhaps underestimating their own ability to adapt -- or pick up a telephone -- just 29% of Facebook and LinkedIn users say they could "probably do without" the popular networks, according to a new study by Anderson Analytics.

Apparently a somewhat less vital recourse, 35% of the 5,000 U.S. social media users surveyed in May said they could do without MySpace, while a more modest 43% thought life still worth living without Twitter.

Under 35, people rely on social networks for "fun" and contacting friends, while older consumers increasingly view them as indispensable for staying in touch with family and close friends.

Correspondingly, the majority -- 75% -- said Facebook was their most valuable network, followed by 65% who cited MySpace. Only 30% said the business centric LinkedIn was their most valuable network, followed by the 12% who gave it up to Twitter.

"Our research shows that Facebook users clearly understand the value of their network," said Tom Anderson, managing partner of Anderson Analytics.

"Twitter's challenge will be to add more value to its service, and LinkedIn's challenge will be to give users reasons to go there more often, something Twitter seems especially good at."

The Anderson report found an estimated 110 million people in the U.S. -- or 36% of the total population -- are regular social networking users.

Of that group, Facebook dominates with 78 million regular users -- defined as those logging on at least once a month -- followed by MySpace with 67 million, Twitter with 17 million, and LinkedIn with 11 million regular users.

While much attention has been paid to the graying of social networks, most users -- 61% -- remain under 35.

MySpace remains the most youthful -- the average age of its users being 29 -- while the average age of Facebook users is 34, and 33 for Twitter.

While it varies by network, the majority of social networkers are now women by a margin of 55% to 45%.

LinkedIn skews the most toward male users -- 57% to 43% -- while Facebook tends a bit toward women -- 56% to 44%.

Men were more likely than women to use social networks for business purposes -- 32% of male respondents said using them for business/career contacts was a key benefit, vs. 22% for females.

Guys are more likely to share information about their hobbies, interesting articles or work-related topics, while gals in general are more likely to share photos, information about what they are currently doing or posts about their pets.

What's more, male users tend to have a greater number of social networking site connections. The report found men have an average of 140 friends on Facebook, 53 Twitter followers and 71 LinkedIn connections; the comparable averages for women are 110, 18 and 36.

Anderson attributes this finding to the fact that males are less likely to be concerned about connecting to strangers online -- 29% for men vs. 10% of women.