My wife, a keen photographer, had recently bought a very substantial zoom lens for her SLR camera. So we took a stroll through Chelsea in London to try out the new kit, taking photographs of people and architecture in the neighbourhood.

At the end of the street I saw a man walking towards us holding a small placard. I grabbed my wife's camera and fired off a few frames. As he came closer to us I realised what I had done.

His little billboard proclaimed that he was being watched by the British security services. When he eventually walked past us, he looked me in the eye, as I stood there clutching the camera sheepishly. By taking his picture, I had vindicated his view of the world.

I think I was more freaked out than he was. There was nothing I could do to convince him that I was not in fact following him. How could I explain to him that by carrying his placard, he was actually encouraging strangers to photograph him?

This extraordinary episode is a useful allegory to illustrate how connected media are not just communicating trends but are actually intrinsically affecting behaviours and perceptions.

Search engines, social media sites and recommendation networks don't just reflect attitudes and consumption patterns, they actually influence them. Google remains one of the very best examples of how the diffusion of ideas and information is accelerated, amplified (and perhaps distorted) through constant feedback online. With search engines in particular, a self-perpetuating cycle can emerge when the popularity of a site improves its ranking in search results. Consequently, the site is found by a greater number of people. Traffic increases and the site's ranking further improves... in turn causing the site to be known to an even greater number of people.  

Only a few years ago, revered soothsayers like Chris Anderson had predicted that the net would 'grow the long tail' in the sense that it would boost demand for and uptake of niche content and products. However, a more striking effect of online connectivity has actually been the exaggeration of mass market phenomena. The tail has certainly grown, as leftfield and quirky offerings have become more widely accessible. However, the 'head' of the distribution curve has also grown. In short; blockbuster, popular stuff (beliefs, products, services etc) have become even more pronounced and widely adopted.

Sales of music albums provide a handy snapshot of how this effect has influenced the growth of mainstream artists. According to the British Phonographic Industry (BPI), albums ranked at Number 1 in the charts are selling more copies than a few years ago. All other positions in the Top 100 have experienced sharp declines in sales.

When you consider how Susan Boyle's career began, with a huge amount of noise online, you can see clearly how the feedback-loop works. The majority of promotion came from user-generated comments, recommendations and links in response to her inaugural YouTube clip.

Similar examples can be seen in books, movies and fashion items. It is unlikely that Harry Potter, The Da Vinci Code and Avatar would have been quite such huge hits in the pre-web era. Rather than killing hyper-populist pop culture, the web appears to be turbo-charging it.

Of course, the flip-side of this online mob behaviour can also been seen with Rage Against The Machine keeping the X-Factor nonsense from reaching the pole position in the singles chart. Self-perpetuating cycles of consumer-generated promotions are infinitely more effective than the most lavish centralised corporate campaign. The combination of the two is genuinely unstoppable.

So, tactically, we marketing folks are eager to stimulate this kind of delicious, democratic chain reaction to promote our wares. Not an easy task. Strategically, there appear to be three options for segmentation and targeting in the web age. Option one is to aim to serve exclusively mass-market groups of consumers. The second option is to focus solely on very specialist niches. And the third option is to aggregate groups of such niches in order to serve larger volumes of consumers. Not a million miles away from traditional marketing principles, eh? The key difference today is the pace and scale that digital media adds to what was once simply called 'word of mouth'. It's possible to go from 'zero to hero' incredibly quickly thanks to the exponential spread of information online. And the journey from 'hero to zero' can be equally swift.

Finally, a message to the guy with the placard: I'm really not a surveillance agent. Yes. People are indeed watching you, sir. But they're more concerned with your mental health than the risk you present to national security.

+STOP PRESS+
Since I wrote this piece, the topics of Google and spying have converged with further news about the search monster slurping up private data from publically available wifi routers. I have some views on this which you can find here.