Pity News Corp. (NYSE: NWS, NWS.A) spent half a billion dollars to buy MySpace, whose profitability rests solely on the attention span of teenagers. Google, Inc. (NASDAQ:GOOG) should take a lesson about its purchase of YouTube. Get your money while you can, because teenagers move on to the next cool thing with lightning speed.

Yuki Noguchi from The Washington Post, wrote last week that the popularity of MySpace, THE required teen social spot last year, is already plummeting in favor of Facebook. Not only purchasers, but advertisers as well, are betting they can predict the social behavior and coolness factors of teens. There aren't enough regression analysis models in all of econometrics to account for such irrational variables.

Xanga, the precursor to MySpace, was THE biggest site in 2003, averaging over 90 minutes per visit per user as teens developed and edited their online profiles or scoped out the profiles of others. In September 2006, the average viewing time of a Xanga profile was 11 minutes. The story is the same with Friendster, which averaged almost two hours of user time per visit in October 2003. In February 2006, average viewer time peaked at just over 3 hours. By September 2006, average viewing time was 7 minutes.

MySpace has already showed the beginnings of a decline in average viewer time. In October 2005, the average viewer time was almost 2 and a half hours. By October 2006, average time had slipped to 2 hours. The up and coming social network site is Facebook, which is still showing increases in average viewer time, now up to 70 minutes per visitor per month.

Among teens, there is very little in the way of brand loyalty. Mostly, teens crave innovation and new experiences within the confines of group experience. Given the increased scrutiny social network sites encounter from teachers and parents, as well as recent negative publicity caused by predators using MySpace, investors and advertisers can expect the next replacement social network site any minute. Too late, it's gone.

There's an interesting piece in the Washington Post about MySpace.com. The title says it all: "In Teens' Web World, MySpace Is So Last Year."

Actually, the author does not provide tangible proof that MySpace.com is going downhill.

No doubt, the site has had a stunning ascent, with over 124 million profiles – and grabbing $900 million from Google Inc. (NASAQ: GOOG). Hey, even if MySpace self-destructs, News Corp. (NYSE: NWS.A) will still have more than covered its initial $580 million purchase price.

However, the author brings-up some good points to consider:

• The history of social networking – especially when focused on teens – is volatile. Some of the prior leaders, such as Friendster and Xanga, are a fraction of their former success.
• There's the creep factor. The author interviewed a variety of teens who are afraid of weirdos who troll MySpace.
• Then there's the authority factor. That is, teachers often go on MySpace to see what their students are doing.
• Also, if key people in a teen's network moves to another site, then many others will follow. For example, a big source of users for MySpace were former users of Friendster.
• Most importantly: Teens bore easily.

Besides, when a site like MySpace gets into mainstream media, can it really be cool any more?

Tom Taulli is the author of various books, including the Complete M&A Handbook. He operates InvestorOffering.com.

For social networking, it's all about critical mass. If you can reach a level like MySpace, you just might be able to get $900 million from, say, Google.

But, the cool thing about capitalism is competition. Big-money deals have a way of attracting a lot of attention. Of course, a swarm of competition is gunning for MySpace (for example, every day, I get about two to three social-networking pitches from PR people). The list has been growing ... Facebook, Xanga, Bebo, and on and on.

Well, the competition is not just local. It's global. Look at the latest splash: Cyworld, which is a wildly successful teen social networking site from South Korea. In fact, it basically owns the market in its homeland.

While MySpace has a clunky -- almost retro -- 1996 look, Cyworld is on the cutting-edge of coolness. Interestingly enough, the appeal is to girls.

The business model is to essentially create a virtual economy.