At home on the road in Europe

In the middle of a cool, cloudless Parisian afternoon, light was pouring into my guest room from a turn-of-the- century courtyard in the 10th Arrondissement. I clambered up to the loft bed and stared at the textiles shop sign swinging in the courtyard through the almost floor-to-ceiling windows.

A bottle of Bordeaux was breathing; other amenities included a stocked pantry and a phone number to call if I needed dinner recommendations or, perhaps, extra shower gel. But I was happy sitting at the window, nodding at my new neighbors as they wheeled their bikes onto the street and headed into the cafe-lined Marais.

Hotel guests pay handsomely for such perks, but I wasn't in a hotel. Nor was I in some vacation rental. I was in the home of Julien Szeps, a 26-year-old chef whom I met through a new kind of short-term rental service called AirBnB.com. And the studio apartment was only 65 euros a night, about $80 at $1.23 to the euro. Not bad for an entire apartment with a full kitchen and bathroom, less than 10 minutes by foot from the Louvre.

While AirBnB is the largest of these new services, it isn't alone. A half-dozen have emerged in the past two years -- with names like iStopOver.com and Crashpadder.com -- offering the convenience of a hotel, the comforts of a home and the price tag of an up-market hostel. Call them social B&B networks, or maybe peer-to-peer hotels.

Social networking first significantly influenced the world of travel in 1999 with the start of Couchsurfing, a service in which members offer a spare couch -- or bed, or floor space -- to fellow Couchsurfers, at no charge. It spawned a social phenomenon, and today counts almost 2 million people in 238 countries as members.

Social B&B networks are a natural next step, imposing an important distinction: money. The new sites appeal to a traveler's desire to see a city through local eyes, but add a hedge against disaster: With Couchsurfing you get what's given (it's free, after all), while sites like AirBnB generally provide detailed descriptions of the private rooms or apartments available for rent.

A three-city test

To book one, I first had to create a short profile of myself. Unlike Expedia.com or other traditional hotel booking services, these sites rely on social networking, and everyone is encouraged to have a face and a little back story.

Next, I scoured its listings. There was a luxury apartment in north London for 65 euros a night and a room in Bloomsbury for 35 euros a night. I opted for a "clean simple room with a chrome silver double bed" near the a train station in the once-seedy district of Kings Cross for 50 euros.

Once you've found your room on Crashpadder, you can interact with the host through the internal messaging system and ask any questions you might have. Hosts can ask for the money either up front or upon arrival.

A week after booking my room, I rolled my bag to a 1920s red-brick council building, where my host, Rachelle Hungerford-Boyle, lives on the third floor. It was the kind of unspectacular housing block that makes up vast swaths of the city, scattered in between the genteel stucco mansions that make it into the films.

I was buzzed through an electronic gate, and found Hungerford-Boyle hanging over the balcony, beckoning me up. I maneuvered my way through a soccer game among 8-year-olds and marched up to meet her.

Protections for travelers

The next morning I caught a Eurostar train to Paris, where my social B&B was booked through AirBnB.com. The site, which is based in San Francisco, was started by Joe Gebbia and Brian Chesky, roommates who decided to rent out their spare bedroom to people visiting the city for a design conference. An idea was born.

In Paris, AirBnB has places in every arrondissement, including $13-a-night rooms in the western suburbs and $285-a-night houseboats on the Seine. As the first website of its kind to grab the headlines, the system has already developed a large and loyal user base. Some properties have as many as 70 user-generated reviews, which give paying guests greater confidence. My studio apartment there had received gushing write-ups, including "peaceful, lovely and so cute!"

After paying $97 for the booking via PayPal, the service sent me Szeps' e-mail and street addresses, and within an hour of arriving in Paris, I turned up in his courtyard, and entered his beautiful studio apartment.

Szeps joined AirBnB this year. "I used Craigslist when I wanted to rent the apartment before, but it was a little too risky. I didn't really know who was turning up," he said. "Then I used a normal B&B agency, but they made the apartment too expensive with their commission, and nobody came."

For the final stop, I caught an overnight train from the Gare Montparnasse to Barcelona, arriving on a beautifully clear Thursday morning. As I walked through the multistory 19th-century apartment blocks, I caught late-rising locals nursing coffees in corner cafes.

I was looking for an apartment I found through iStopOver, a year-old site based in Toronto that specializes in providing housing during large events like the World Cup and the Olympics, when visitor demand outstrips the supply of traditional hotels and B&Bs. The "Barcelona Penthouse" looked a little less homey, and more like a traditional vacation rental, than other listings, but I drooled over its outdoor terrace.

It was also in the Eixample neighborhood -- a 15-minute walk from the tourist-drenched sidewalks of La Rambla, though it feels like a different city. There are no street performers or tacky stalls, just motorbikes parked outside apartment buildings with staggered roofs.

I buzzed an intercom two doors down from a tiny corner cafe, and was greeted by Arian Mostaedi, a 30-something publisher of coffee-table design books, who guided me through his modern one-bedroom apartment, with a glass kitchen table, a sparkling bathroom with a glass shower stall, and a queen-size bed. And bingo -- the large roof terrace with lounge chairs shrouded in citrus plants. For $105, it was a bargain.

After the brief tour, I gave Mostaedi the code that allows him to collect my payment from iStopOver. That's one of the safeguards that iStopOver offers to guests. If a listing turns out to be fraudulent or misstated, you can refuse to give the owner the code, and the fee is refunded in full. Other services offer similar protections: AirBnB withholds a host's payment until 24 hours after guests check into an accommodation in order to fend off potential scammers, and Crashpadder uses credit card payments to verify guest identities.

I spent most of my stay in Barcelona sprawled on my rooftop terrace, dipping in and out of the apartment for cold drinks and sliced fruit. I napped on a bed surrounded by exotic patterned pillows. As the sun faded, a text arrived from Mostaedi, asking if I needed anything.

"All is good," I replied, as I watched my own private slice of Barcelona skyline turn from orange to red to blue.