Close-Up: Live issue - How advertisers embraced the widgety world.

Widgets are allowing advertisers to develop a more comfortable relationship with social networks' users.

Anyone who attempts to pin the genesis of a huge media phenomenon down to a place, a day and a time, almost to the minute, can end up looking very silly indeed. But here goes. Widget frenzy began at 3pm (local time) on 24 May 2007, at the San Francisco Design Centre.

That, give or take a second or two, was when the founder and chief executive of Facebook, Mark Zuckerberg, ambled onstage and announced to an audience of around 750 web developers and technology bloggers - the latter tippety-tapping furiously on their laptops - that Facebook was to allow absolutely unrestricted access to widget developers. And Jiminy, while they were about it, they decided to push the boat right out - Facebook's software engineers would even be allowed to work with outside developers.

Few doubted that this would lead to a surge in activity. And hasn't it just - the numbers are mind-numbing. According to the monitoring company Adonomics, by mid-April 2008 there were 21,800 widgets in use across Facebook, and the total number of installs was in excess of 898 million. In any given 24-hour period, these widgets were being used a combined total of more than 34 million times. There were 200,000 developers with material either up and running or in development. By the time you read this, though, these numbers will be hopelessly out of date.

And, of course, given the magnitude of the phenomenon, it's almost unclassifiable. A web widget merely allows you to place an area of customised functionality (essentially a mini website) within another site. Facebook's most popular widget is Fun Wall, an uber-widget that makes it easier to share videos and games. This, however, is a phenomenon with a very long tail - how could it be otherwise when there are so many of the things out there? Many offer compelling functionality; others are largely decorative.

That's just on Facebook. Other social network platforms have had to follow suit in opening up. And this is not just about web widgets either: the Zuckerberg-inspired web widgets have also reignited interest in desktop widgets.

Tellingly, advertisers are interested in both types. Very interested indeed. Enthusiasm for web widgets was, in the earliest days, a result of nervousness about whether traditional online advertising formats were at all appropriate in the social networking space. Indeed, there have been a number of Facebook groups set up to oppose commercialisation of the site.