This week, Trendsurfing is committing itself to making the world a better place. There’s only one teeny condition: you must do so, too, otherwise the deal is off. It’s a beguilingly simple moral equation, which, thanks to a wave of internet-based networking clubs, is being tested with a burst of fascinating real-world examples. Whether you’re a political activist or a public-spirited fundraiser, online "promise exchanges" are suddenly the fashionable tools for making a difference.

Here’s how they work. Let’s say you have a goal that can be achieved only collectively – a mass boycott of a rip-off bank, say, or a call for multiple donations to fund obscure medical research. By publicly signing up at sites such as Fundable (www.fundable.org), supporters commit themselves only if a specified number of others do the same. And if they don’t, signatories take back not only their original offer, but the satisfaction of having at least tried.

Economists call this conditional commitment an "assurance contract", a concept that political activists in particular have been eagerly embracing via the web. The most ambitious experiment so far is the Free State Project (freestateproject.org), an attempt by American libertarians to build a minimally regulated society in New Hampshire in which to "live free or die". Only when 20,000 supporters have signed on is each of them solemnly obliged to up sticks – enough, the thinking goes, to make Uncle Sam think twice before storming in to re-impose order. Still, last week, the revolution remained 13,414 freedom-lovers short of a quorum, suggesting that New England will be spared civil war for a couple of years yet.

In Britain, political activists have taken a more sedate approach. At PledgeBank (www.pledgebank.com), a promise exchange from the public-spirited geeks behind FaxyourMP.com, users seem more concerned with finding lost dogs and planting trees to offset their personal carbon dioxide emissions. Still, in its first few weeks, some intriguing early pledges have attracted enough support to prompt action. Nick Jones, a Manchester United supporter, vowed to boycott the team’s sponsors while Malcolm Glazer remains in charge, but only if 50 other people joined him. Two weeks before his deadline, Jones had attracted 170. Other groups have agreed via PledgeBank to register en masse as bone-marrow donors, clean the River Taff and, following a pledge by Tom Steinberg, lobby MPs for free wireless internet in the British Library.

"We all know what it is like to feel powerless," explains Steinberg, one of the site’s creators. "PledgeBank is about beating that feeling by connecting you with other people who also want to make a change, but who don’t want the personal risk of being the only person to turn up to a meeting."

Could these sites become the eBays of political dissent? Their potential is already being tested. One PledgeBank user, Phil Booth, has signed up 4,000 opponents of ID cards to promise civil disobedience if the scheme gets off the ground. The commitment comes into force if the total reaches 10,000. At that point, presumably, the Government will enact a one-mile exclusion zone around every computer in Britain. Personally, I’d protest by streaking down Whitehall – though only if a million of you promised to join me...

david.rowan@thetimes.co.uk

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