Who do you trust for holiday recommendations? Your friends? A travel agent? A travel writer? Friends’ suggestions are often outright winners, because they know your likes and dislikes. And in the brave new world of “Web 2.0”, it no longer matters if your friends haven’t been to the places you want to visit – because the growth of social networking sites means you suddenly have friends all over the world.

A new wave of travel websites is enabling travellers to hook up and swap information in such large numbers that traditional holiday companies are having to sit up and take notice. In the US, such sites include www.igougo.com, www.gusto.com, www.tripmates.com and www.tripconnect.com, but the buzz in Britain is all around www.wayn.com, which stands for Where Are You Now? It has grown from 45,000 registered users in summer 2005 to 7 million today.

Last month, it attracted $11 million from investors including Brent Hoberman of Lastminute.com and David Soskin, CEO of Cheapflights.co.uk. “WAYN is networking on steroids,” said Hugo Burge, vice-chairman of Cheapflights and another investor. “You can speak to people who are living where you are going, or have been there, which is a very powerful concept.”

The power of social networking sites such as MySpace or Bebo – and which WAYN is applying to the travel arena – is that they foster a huge sense of trust in the opinions of their members, who post detailed profiles about their own likes and dislikes. “Why do you trust a website?” asked Walid Al Saqqaf of www.trustedplaces.com, which launched in September to enable people to post tips about their favourite places in London.

“Because you can click on people’s profiles to find out more about them, and so you assign more trust to them if you share similar tastes.” Perhaps realising it was missing a trick, www.tripadvisor.co.uk has, since October, allowed users to add personal profiles. And in general those posting comments do not have a vested interest in the places they describe – sites claim to monitor and remove bulk or overenthusiastic comments posted to talk up a particular hotel or restaurant – which also helps to build trust.

Travellers were of course among the earliest adopters of the internet, using cyber-cafés instead of the Poste Restante, and early bulletin boards such as Lonely Planet’s Thorn Tree to swap travel tips. Now “Web 2.0” sites (on which users create content and exchange views, instead of passively receiving the site’s information) are creating a growing community of travellers whose inclination is to eschew, or at least take with a pinch of salt, the advice of authority figures such as travel agents and writers. The traditional guidebook is also coming under threat from www.wikitravel.org, whose users are creating a constantly updated guide to the world.

Smart travel companies are using these sites to improve their business. They spot the targeted advertising opportunities offered by a site such as WAYN – where, for example, they can discover that 500 people in the Oxford area are thinking of going on holiday to the West Coast of America. Foolish is the travel agent not already monitoring TripAdvisor to check the hotels it sells are getting a good press, or the tour operator that fails to keep an eye on www.holidaysuncovered.co.uk or www.holiday-truth.com for reports from mainstream resorts that may alert them to potential problems.

Social networking sites offer a great new research tool to the canny traveller, but they are unedited, anecdotal, unaccountable. As in the real world, the people you meet through sites such as WAYN could be dull, untruthful or unpleasant. Travellers who plan their trips based solely on the advice of their online friends may have the time of their lives – but will have no comeback if they find they have been misled. But at least it’s better to fall out with an online friend than a real one.

Times recommends

• 10 of Rough Guides' best images
• How to do Florence for free
• The UK and Ireland's 25 best Christmas events