Facebook is this month's craze du jour. For those who have been vacationing on Mars, it is a semi-respectable social networking site founded by a Harvard student named Mark Zuckerberg to offset the social frigidity of that august institution.
In its early period, it grew steadily as a virtual space for students across the United States.
To join, you had to have an email address from a recognised higher-education institution. This placed Facebook beyond the purview of the mainstream media, in comparison with, say, MySpace, which would take anybody, and did. But then Facebook opened its doors to all comers and has been growing like, well, MySpace.
At this point, big media woke up. News editors began barking: "What's this Facebook thingy? Go find out."
And what better way to find out than by signing up? So the numbers of hacks appearing on Facebook increased rapidly and the space was filled with their touching requests to one another to become "friends". They found - to their surprise - that they rather liked this social networking business once they got the hang of it.
A case in point is the BBC's technology correspondent, Rory Cellan-Jones. Researching a story about social networking, he joined Facebook, then did an interesting report for the Today programme, in which he said he had few "friends". Next time he logged into Facebook, he discovered that a group entitled "Befriend Rory Cellan-Jones" had been set up.
When I last checked, it had 468 members. It was followed by the "Not Bovvered about Rory Cellan-Jones" group, then by the "Rejected by Rory Cellan-Jones" crowd (those whose request for friendship was spurned).
All of which may explain why Cellan-Jones appears to be spending a lot of time inside Facebook; every time I log into the site my news feed relates all the things he has been doing. Why? Because I am one of his "friends" and Facebook keeps me abreast of what my friends have been up to.
Cellan-Jones has, for instance, been posting videos and photographs, joining groups and leaving notes about what's happening in his day job and his personal life. I see he has joined the "Mark Kermode Appreciation Society" and "is home after exhasuting [sic] round of socialising".
Facebook is growing so rapidly that Rupert Murdoch, proprietor of MySpace, is concerned. MySpace, you see, is really a site for young persons - which is why its average personal page has the visual and aesthetic appeal of a teenager's bedroom floor.
But most teenagers grow up, and presumably learn how to tidy their bedrooms, so the US$1.6 billion ($2 billion) question is: where will they go when they tire of MySpace? The disturbing thought that has occurred to Murdoch is that they might go to Facebook.
But it isn't just the age dimension that marks out Facebook from MySpace. A contrast in strategic vision is also becoming apparent.
Murdoch bought MySpace because it had become one of the most visited sites on the web. The challenge for the Murdoch team was how to "monetise" those eyeballs. Their solution was a traditional combination of advertising and control (it also helped that Google paid US$900 million for the privilege of providing search facilities on the site). The advertising bit is self-explanatory; the control freakery is exemplified by the Murdoch philosophy of not allowing other people to make money on his platform.
Recent developments suggest Facebook has an alternative strategy - that of providing a platform on which other people can deploy their ingenuity and perhaps make money. At any rate, a few weeks ago Zuckerberg published the site's API, the technical details which enable programmers to write applications which interface seamlessly with Facebook.
The result has been a deluge of small applications enabling subscribers to do simple things such as add music to their profiles or share information about favourite books. If this works, Facebook might grow into an ecosystem - much like eBay - and Zuckerberg will become the richest Harvard dropout since Bill Gates.