It begins harmlessly enough. You're chatting to a friend, a neighbour perhaps, over the garden fence. The conversation turns to her upcoming wedding. What would she like for a present?

Suddenly a giant box of toasters falls from the sky, landing with a crunch between you. You can no longer see your friend. You start to scramble over the debris, the crushed cat, to find her - is she ok? - but then something small and hard hits you right in the eye. You pick it up: it's a diamond ring. Then another hits you in the back of the head. You're under attack!

You start to run, leaping over fences and through conservatories, but you know you're being chased. Hunted. A guy pops out from behind a tree with a megawatt smile: "Looking to buy some trainers?"

"Get away!" you scream, desperately weaving round him.

"Get away from it all!" a voice from nowhere booms in your ear.

You jump. Where the hell is it coming from? Is it IN YOUR HEAD? You hear it again, ingratiating now, soft, a warm current in the frosty air. 

"A Thompson holiday is only a click away."

And so it begins. Twitter is getting a new API, or “application-programming interface”, a technology which will make it easier for advertisers to reach the right customers. In other words Twitter is getting what Facebook got back in 2010. Advertisers will be able to access information you release in the course of social interaction, and use it to sell you things.

This makes sense for Twitter, for now. It has a great product, (after all, all decisions have hitherto be made with customer experience in mind) and now it wants to make some proper money.

Here's the FT [2] on the financial benefits of the move:

A similar technology launched by Facebook in 2010 helped that social network reach more than $3bn in revenues the following year, with analysts estimating the system currently generates roughly 60 per cent of the company’s revenues.

eMarketer estimates that with the new venture Twitter's revenue will grow 90 per cent this year to $545m, and that  it will earn over than $800m next year in global ad revenue.

But what of the product itself? Twitter spokespeople insist the user experience will be uninterrupted "in the short term" - users may not see that many more ads - but that's not the whole point. The really damaging aspect of the new advertising development, I'd argue, is that it'll allow ad companies to "target" their marketing.

"Because we have a robust listening solution and engagement solution, we can listen to what people are saying [on Twitter about a brand] and engage with them and take any of their tweets and promote them," s Salesforce Marketing Cloud's  Michael Lazerow told ADweek [3].

But social media sites are a great deal about trust - you are downloading a large amount of subtle personal information (you can't help it, you're socialising) - and it's an uneasy feeling that cynical sharks are circling, trying to make money out of it.

You get too much of this on twitter anyway. Tabloid journalists haunt the edges, looking for someone famous to make a a false step which they can use out of context. Now imagine what would happen if everyone's witterings were that lucrative.

But we don't really have to imagine - we have Facebook. Since its 2010 marketing drive the site has been haemorraging users (it lost more than $50bn after last year's stockmarket crash), and those still on it squirrel away that valuable personal information, using it mostly to arrange social events via private messaging.

So what today's Twitter news really means is that another great social networking site has peaked and is on the way down. Plus ça change.