IT SEEMS like a lot to pay for a glorified noticeboard. Particularly one that is thought to cost more than a million dollars a month just to keep running and which has been long-regarded as a copyright lawsuit waiting to happen. But Google's recent acquisition of the video-sharing site YouTube for a not inconsiderable $1.65 billion created some curious consequences for music - and still more ramifications for dancing.

Let me explain.

Despite a winningly simple interface and some of the best short videos of pets using the toilet that you're ever likely to find, YouTube doesn't immediately look like a wise investment. It's never had much of a business model and, on paper at least, possesses few appealing assets. What it does have in abundance are users - or "broadcasters" as the company likes to call them - and a worldwide audience of more than 70 million.

You can watch almost anything on YouTube, and little of it counts as quality broadcasting: television show snippets, dodgy concert bootlegs shot with mobile phones, pieces of dough exploding in a microwave. But the mainly teenaged demographic ensnared by YouTube has rallied around two programming strands in particular: confessional blogs by young girls in their bedrooms, and anything in which people lip-sync to music or dance like loons.

One of the most popular videos ever posted on YouTube involves two Israeli girls, known only as Tasha and Diska, slinking around a bedroom while lip-syncing to the Pixies' Hey. The video is defiantly lo-fi, but so brisk and considered in its editing that it almost seems like a violation of programming standards. Recently it was parodied by self-described "amateur film-maker" Kevin Smith in an amusingly shameless effort to attract YouTubers to Clerks 2.

Why has the Hey video been viewed more than 10 million times? It's hard to say. But the girls offer their own cogent explanation: "Dancing stupid is fun."

Whatever effect Tasha and Diska's moves have on the Pixies' back catalogue, their home music video represents a new era of permissiveness for the music industry. In the days before YouTube, such use of copyrighted material would have resulted in an avalanche of cease and desist messages from a label's lawyers.

One reason YouTube hasn't already been sued for copyright infringement is that, until now, there's never been anyone with any money behind it to sue. What may continue to protect the wealthy conglomerated GooTube from such bother, however, is the current desperation of a music industry battling for its survival.

Before the acquisition, each service struck deals with different record labels: YouTube, for instance, has licensing deals with Warner, Universal and SonyBMG. In exchange for sharing its ad revenue, YouTube can host an ad-hoc archive of music video gems, most of them retrieved, digitised and posted by an army of fans for the benefit of posterity. Posterity, however, may be more interested in four guys hopping manically between several whirring treadmills.

So far, the undisputed breakout music stars of YouTube are OK Go, an eccentric and maddeningly catchy rock group from Chicago who are experts in concocting loopy DIY dance crazes. Their self-choreographed, super-cheap homemade video for A Million Ways is, apparently, the most downloaded music video ever (more than 9 million transfers), although there is now fierce competition from their self-choreographed, super-cheap homemade video for Here It Goes. In this inspired bit of goofiness, the bass player rather than the singer mouths the lyrics, in accordance with YouTube's lip-syncing aesthetic.

Repeating the feat live for the MTV Music Video Awards this year, OK Go seemed to bring the strange evolution of the music video full circle.

And this is only the beginning. Right now YouTube is running with videos of a new dance craze called the Ratchet. As far as Discotheque can work out, this involves waggling your elbows a lot and generally behaving as though all your bones have been replaced with spaghetti. The interpretations vary from person to person but the song (Lil Boosie's Do tha Ratchet) never changes. Before the year is out Lil Boosie may have more music videos than anyone in history.

These fan-created promos are becoming the true measure of success in contemporary pop, turning YouTube's broadcasters into musical participants rather than merely consumers, and boosting the popularity of songs in the process. But there is something still more cheering about the YouTubers. In a virtual age, where music exists only in long strings of ones and zeros, and bricks and mortar retailers topple into bankruptcy, the dancing stupid craze broadcasts a reassuringly tangible message: Let's get physical.