Some older readers may recall a time when Justin Timberlake was just a pop singer.

Those old timers may also use an antique website called Facebook, and they might be shocked to learn that Timberlake is the new owner of an even older social media site called Myspace.

Few would remember Myspace at all if wasn't for the fact that Rupert Murdoch bought it and lost a lot of money.

Murdoch's News Corp paid US$580 million for the site in 2005 when it was the happening place to hang out on the net.

Six year's later and Murdoch's personal brand of cool has inexplicably failed to add value to the site.

Something called Specific Media has snapped it up for a mere US$35 million and will be hoping that, as one of its shareholders, Timberlake will do a better job of bringing street cred to the business.

Whether he proves cooler with the kids than Murdoch remains to be seen.

But the story ought to highlight the risk of over-inflating website values which are seldom much more than the current worth of their brand.

And as brands go they are pretty volatile given they tend to cater to customers that are young and fickle.

You might think the last tech bubble - which burst in 2000 destroying billions in investor wealth - should provide warning enough, but 10 years is clearly far too long for the collective memory of the market.

Even the Myspace story has failed to halt the soapy ascent of a new bubble. A business focused networking site called LinkedIn was floated on the New York Stock Exchange for about $5 billion last month and is already being described as underpriced. Its shares had already doubled in value as of yesterday.

Meanwhile, analysts have suggested the number one US site for movie downloads - - should float with a price based on a multiple of 50 times its earnings.

That's huge. Many of the big private equity deals that have come unstuck in the past few years did so after being done on multiples around 20 times earnings. Mature companies that make real things and return real dividends to shareholders mostly sell on multiples in the teens.

Big multiples suggest great confidence in growth potential but when analysts start talking about figures like 50, sane investors should run for the hills.

This month, stories have been flying that Facebook could float on the market with a value of more than US$100 billion. This is at the same time as some tech commentators warn that the site may have already peaked in popularity.

News that Facebook is over the hill might also shock those who are just getting to grips with the "status updates" and "liking" things.

The site is still going strong with an older generation keen to stay in touch with their children as they party around the world. Maybe that's what's killing it - you can't "unfriend" your mum.

All of a sudden you have to think twice about posting those dodgy jokes or photos from your weekend away with the boys.

Facebook rival Twitter seems more securely embedded in the hearts of the tech elite although talk about its market value tends to be in the US$10 billion range.

That might be because it hasn't pushed as hard as Facebook to generate revenue off its followers by offering information to commercial interests. That's another issue that some say is hurting Facebook.

It highlights one of the big problems with the valuations on these companies. A model which allows them to generate enough revenue to turn a profit without scaring off users remains far from clear.

That didn't stop Google entering the fray this week with a new site called Google+. At first glance it looks to be taking on the family friendly Facebook rather than more Spartan Twitter.

As a point of difference it is offering tighter privacy provisions - which again raises that question of how it makes money.

It also lets you put all the different followers you have in different groups or "circles". So you create a family circle and a work circle and a friends circle. Then you can start posting those dodgy jokes again but only let those in one or other of the circles read them.

Whether these kind of innovations are enough for Google+ to reach a critical mass will depend on how the early adopters - the kids and web geeks - take to it. No amount of mainstream marketing can ensure success in a virtual world where every critic can publish opinions at the click of a button.

Even if talk of bubbles is unfair, this week's frenzy of activity suggests we are in the grips of another tech boom - and what's wrong with that? The global economy could use an innovation-led boom after years of speculation in property and commodities. But what new technological breakthroughs are we dealing with here?

Social media sites have hit a critical mass and are changing the way we interact with each other. That puts them in a similar space to mobile phone companies and email providers in the 1990s and 2000s. But how they will generate tangible new wealth isn't so clear.

They may allow us to communicate more quickly and more efficiently, we will connect more easily with customers or retailers but what they offer is a means not an end.

Ultimately they offer no new paradigm in a world that is crying out for technological breakthroughs in the production of energy, food, medicine, transport and any number of basic human needs.