When she visited Beijing this past April, Sandra Smith got an insider's tour of the city's Capital Museum, a traditional Chinese meal, and a spare room to sleep in for a night -- all for free, and all thanks to perfect strangers she met online. "It was priceless," says Smith, a 57-year-old retired psychotherapist from Birmingham, Ala. Particularly, she says, "when you think that just a few years ago" in China, "you had to have a minder and could only see what they wanted you to see. And I had this family willing to talk to me extensively about everything from child-rearing philosophy to why they wear red at weddings."What Smith describes as "the best experience I had in three weeks in China" was thanks to CouchSurfing.org, a website whose name has become shorthand for an outside-the-guidebook hosting movement that's swept the travel world. CouchSurfing has some 2 million members in 230 countries or territories willing to share their couches, spare rooms, or even backyard tents. One Fredericksburg, Va., traveler got his own apartment in Amman, Jordan -- his host hadn't moved in yet.CouchSurfing.org was conceived when Casey Fenton, then 25, booked a trip to Iceland without a place to stay. He spammed the University of Reykjavik student E-mail directory, looking for someone to put him up and show him around. The CouchSurfing website, which Fenton and others started in 2003, is a variant of traditional hosting clubs that facilitate stays in private homes and have been around long enough to qualify for AARP membership. The pioneer, Servas International, was founded in 1948 to promote "international understanding" by encouraging people to stay with local hosts when traveling.However, CouchSurfing.org has dramatically increased the popularity of hospitality exchanges in part by integrating Facebook-like profiles into the process, so prospective hosts from Paris to Portland, Ore., can get a better sense of who might be coming to dinner (and vice versa). CouchSurfing also pulled the process onto the Internet, allowing easier correspondence and reference-checking. Some homestay groups simply offer couches or a place to sleep, but others require hosts to put up guests in spare rooms and provide breakfast. All offer friendship and cheap lodging along with loftier goals.At Servas, which is recognized by the United Nations as an affiliated organization, the motto is Gandhi's maxim: "The best way to find yourself is to lose yourself in the service of others." The couch-surfing ethic encourages participants to think of themselves as ambassadors for their hometowns and countries. Smith's Chinese hosts have planned a trip to the United States and will stay with her family.One should not imagine, though, that couch surfers are simply 20-something backpackers sleeping in a corner on a dirty floor. Smith acknowledges that she was initially suspicious herself, considering she had first heard about the practice from a 23-year-old relative. In fact, it's a multi-generational phenomenon."It's long been a trend for retirees -- you could even say they started it themselves," says Lauren Braden, 36, of Seattle, who cites the Affordable Travel Club (members must be over age 40; most are over 60) as her inspiration for starting her own hospitality exchange, Casa Casa, in 2009. Braden coveted the camaraderie and cheap sleeps of ATC—founded in 1994 and currently managed by her mother -- but wasn't old enough to join. (Casa Casa's minimum age is 24 and its members range up to age 87.)None of the clubs expect you to enter a lottery to determine where you will sleep or the age of the company you'll keep. In clubs open to all ages, you can still search for a host by age. Although only 3 percent of CouchSurfing.org's membership is over 50, that's still more than 60,000 people. And in the host's profile, you can see a photo or description of the type of accommodation being offered.CouchSurfing is completely free. Other clubs assess small fees for accommodations (not more than $20 per night) and set higher "quality expectations," Braden acknowledges. But all the groups have their hidden gems. Miami entrepreneur Tau Jonty Braun, 37, once stayed at a retired senator's lake house, sailing and obeying his host's instructions to "eat, sleep, and wait to eat again."Safety concerns. The key question for most people is safety. All of the hosting organizations take precautions. Servas, for example, requires a lengthy interview for both hosts and guests, while CouchSurfing relies on references from fellow members who've hosted or stayed with the person and symbols showing levels of trustworthiness (like eBay's verified sellers). Some people think a bit of money changing hands makes the bed-and-breakfast hospitality exchanges (like ATC) safer. "I think people need to pay for what they get," or some will "seriously take advantage," says Mary Carol Haggerty, 68, of Westbrook, Maine, a member of both ATC and Casa Casa. "Twenty dollars is enough to make people think twice about being sleazy."When examining profiles, Smith suggests "reading between the lines a little bit." She points to one where reviewers said the guy was not very communicative and "didn't arrive with the funds we would have expected that he would have to take care of himself." And although she thinks it's "fun to hang out with younger folks," if she reads about how much they party or love alcohol, she moves on. Couch surfers may also want to keep in mind these tips:1. Leave plenty of time to investigate -- and to be investigated -- no matter which site you choose. Smith joined a group hoping to stay in Copenhagen the following week, but learned that "one really needs a history of interactions and a reputation." How to get one? Consider meeting up with other couch surfers in your town, who can provide your first references.2. Don't travel without expecting to host, even if your club doesn't require it. "If you've stayed with other people, but your profile doesn't have any references from people who've stayed with you, it smacks of freeloading and the community frowns on that," says Isabelle Finck, a 64-year-old couch surfer from Minneapolis. Interestingly, some join simply because they like hosting. Tom Henninger, 63, of Tampa, doesn't travel himself, but enjoys having international guests because it's "travel without the rough bits," he says.3. Don't count on hosting to be a money-making venture. As noted, CouchSurfing assesses neither membership nor guest fees. Other clubs charge only for membership. Those that set small nightly fees merely expect the host to be paid in cash at the end of the visit. That said, most hosts say they usually enjoy their guests so much that they almost forget about the money (though the travelers produce it in the end).Haggerty suggests that first-timers introduce themselves as such in their initial E-mail or phone call. "Remember that the people you're visiting or hosting have probably done both themselves, so they understand," she says. "Sure, it's daunting. But most things in life are when they're brand new."