Many environmentalists subscribe to a view known as "peak oil" -- a term used to describe an inflection point in history in which half of the oil that exists in the world has been used. From the moment peak oil has been reached a fossil fuel-based economy will enter a downward spiral eventually leading to a situation that few care to contemplate.

Facebook may be rapidly approaching a phenomenon we might call peak hype -- the moment when both usage and investor interest Facebook reach their zenith and rapidly start to decline and spiral downward toward a fate that few investors in Facebook would really want to contemplate.

One could argue that MySpace entered peak hype shortly before it was sold to Ruppert Murdoch and News Corp. for $580 million in 2005. News Corp. sold it just a few years later for $35 million. One could also argue that much-hyped tech IPOs of Groupon and Pandora also marked their moments of peak hype. During a period when the stock market was on a tear, both Groupon and Pandora have been sinking fast. Their stocks are now trading at less than half their value on opening day of their IPO. LinkedIn has maintained it value during the same period, largely because its demographics and user base make it much more amenable to commercial and professional activity, which is more easily monetized, than Facebook's informational flow.

Many dismiss the notion that Facebook would suffer a similar fate to MySpace, Groupon, Pandora or Friendster, citing Facebook's impressive technological prowess and growing user base. But it is worth noting that while user and usage continue to grow, the pace of growth is leveling off. Where are the future areas of growth: India? China? Both problematic. It would not be surprising to see users and usage actually start to decline within a few years, as some of the factors I describe below start to take effect.

If one scratches beneath the surface of reported events, one can start to see several clear reasons why the coming Facebook IPO will one day be looked back on as Facebook's moment of peak hype. Here are an 13 unlucky reasons why potential investors in Facebook should pause for reflection before jumping in.

1. The value of time being spent on Facebook is increasingly being called into question. There have been a spat of recent reports suggesting deleterious health and psychological effects of Facebook. These reporsts suggest that Facebook time is worse than wasted time. People who spend a lot of time of Facebook are exhibiting the tendencies of addictive behavior. School officials, parents and employers are all concerned and one can expect societal sanctions to be imposed by authority figures who rightfully recognize that time spend on Facebook represents an unhealthy and unproductive diversion.

2. The demographics of Facebook won't support ramped-up commercial activity. Most of Facebook's users are young and have very little disposable cash. They're the kind of people who have lots of time, and well defined social networks, but they're not the kind of people who are likely to click on links to ads or eventually buy anything from within Facebook's walled garden.

3. Social is not commercial. Most people use Facebook to share and exchange social information and photos. They're on Facebook because they want to engage is social activity, not commercial activity. A recent Wall Street Journal article cited numerous advertisers who were questioning what they're getting by advertising on Facebook.

4. Mistrust of Facebook is growing at an alarming rate. While attempting to quantify trust is an exercise fraught with difficulty, anecdotal evidence suggests that thought leaders increasingly are suspicious of Facebook's modus operandi. The Facebook IPO, with very public discussion of the pressures on Facebook's management team to "monetize" the information flow in Facebook, can only serve to further erode what precariously level of trust that now exists between users and the company that controls all that information.

5. A high percentage of Facebook profits come from endangered species. Fifteen percent of Facebook's revenues and a much larger percent of its profits come from the sale of Facebook Credits to Zynga, for which Facebook takes a whopping 30 percent cut. Zynga, the developer of Farmville, Cityville and other online games, then sells those credits to users who buy things such as virtual pigs with those credits. Two big questions here: Are virtual pigs an endangered species? In other words, how many virtual pigs are people are willing to buy with Facebook credits? What if Zynga develops its own payment system and cuts out Facebook when their current agreement expires? Google has has developed a competitive credit system, from which they only take 3 percent cut. How sustainable is a business model that takes 30 percent when competition is only charging 3 percent?

6. Social sharing is inherently limited. With a built-in imperative to keep increasing the number of friends you have on Facebook, the incremental value of each additional friend diminishes. Many of those who become "friends" on Facebook are really not friends in any traditional sense. Often they're not even acquaintances. As the meaning of friendship becomes diluted, the value of recommendations from faux friends diminishes. This phenomenon often leads to "Facebook fatigue" or, in extreme cases, "Facebook exhaustion."

7. International users are not big spenders. Most of Facebook's recent growth is coming in countries where users have very little money to use on Facebook. In China, with the standard of living much lower than that in the United States, it is unlikely that Facebook users will be the kind of users that Wall Street wants.

8. Serendipity is different from search. Most of what people see on their Facebook wall is serendipity. It's random information that increasingly is becoming a jumble. One of the reasons Google is so profitable is that when someone searches they are actively looking for something and thus more likely to want to click on an ad that appears. Serendipity is not search. People who stumble upon something on Facebook are much less likely to be commercially motivated to click on a link that will eventually lead to a purchase.

9. Privacy is becoming more and more important. As Facebook approaches (or crosses) "the creepy line," regulatory bodies, watchdog groups and users will all become increasingly concerned about Facebook's privacy policies and their head fakes. The net here is that legislators will be taking an much more proactive role in regulating what Facebook does with user information.

10. Facebook's reported IPO price is not supported by the numbers. At $100 billion valuation, Facebook would have a 100:1 price to earnings ratio -- the kind of PE ratio that is only reserved for tech companies on the early stages of their growth trajectory. Facebook is no longer in the early stages of growth. It is a mature network whose warts are becoming all too apparent to anybody who takes a close look.

11. Patent challenges are likely. To build out their technological platform, Facebook's engineers were on a tear. They built what they felt the market was demanding, often with insufficient attention paid to possible infringement on existing patents. One can expect more and more patent challenges to what Facebook has built, all of which will have the effect of miring Facebook in legal battles that will sap vital human energy and financial resources. To continue buying patents will be a cash drain on the company. Defending itself in patent lawsuits will be a drain on management time and energy.

12. Social networking is still a black box. Perhaps the most troublesome factor is that nobody yet really understands this phenomenon we call social networking. We don't understand its underlying dynamics. We don't understand the limitations of networks and we don't understand the trajectories of growth and contraction. For years people have accepted Metcalfe's law at face value. That law holds that the value of a network increases geometrically in proportion to the size of the network. But all networks are not the same. Is a telcom network the same as a social network? We don't know, and $100 billion is a lot to spend on something we know so little about.

13. Facebook has a flawed capital and management structure. Mark Zuckerberg owns 57 percent of Facebooks voting shares, leaving the company decision making structure in the hands of a 27-year-old who, prior to Facebook, had no business experience. He also has yet to live through tumultuous market activity that more seasoned executives have experienced. One of my friends, who trades stock for a living and has done quite well, sums up the secret of successful investing: "It's all about cash management. You need to make sure you always have enough cash to survive the downturn and can be able to invest tomorrow." Zuckerberg's impulsive decision to spend $1 billion on the acquisition of Instragram, a company with no revenues and 13 employees, without substantive consultation of his board could be a sign of genius, but more likely it's a red flag about Zuck's negotiation style. Will Zuckerberg's total control of voting rights and limited business experience hurt the company? Only time will tell.

Add all of this up and you have a classic situation of peak hype. Facebook has been an amazing success story and most of that success is well-deserved. But investors are well-advised to take a closer look at the underlying drivers of Facebook's success, and ask themselves whether there are limits to their growth, just as environmentalists are increasingly asking whether there are limits to growth of an ever expanding economy on a planet of finite diminishing resources.