Bottom line, the article is talking about growth in revenue and income. The article outlines that growth can come by two ways: growth in the number of users and the growth in $/user. It claims that the former has little upside because of how large Facebook already is. It raises questions about the latter.
In many ways, for the man on the street Facebook isn't a good investment. At the same time, it doesn't seem to be a goal of management to create a company that entices investors. See the line "we make money to create a better product, not create products to make money."
Doesn't that say it all?
E.g., suppose Facebook's equity takes a significant decline in value on the public market: employees become unhappy as the equity component of their compensation declines; Facebook's ability to make large acquisitions becomes more expenseive when its stock is worth less; and its ability to raise capital diminshes because it's more expensive to borrow exactly because their financials aren't as good, according to their stock price.
I personally believe that the long-term goals of investors and founders are very well-aligned. I believe that the common statment by founders nowadays, that they are building a company not for their investors but for their users, will produce the long-term financial results that investors want. It's the short-term goals of investors that conflict with that.
In short, equity isn't this isolated thing that can be happily ignored. It's tied to everything.
So Zuckerberg cashes out at Facebook's peak, leaving the subsequent 'investors' with nowhere to go but down. I wouldn't necessarily put that intention past Zuckerberg, and perhaps a Facebook collapse would be a good thing for openness and interoperability on the web, but isn't it a bit of a self-defeating strategy? Can the hype machine generate enough naive investors to generate a substantial cash-out?
I'm surprised so little is made of dividends. Growth has faster and sexier return, but will fail sooner than long-term steady well-maintained income. $5/user may not be much, but it's better than $4 and falling. Focus on maintaining long term loyalty; there are a lot of newcomers bent on seducing current users away.
The present value of a perpetual annuity (to keep things simple) is C/r where C is the recurring payment you get, and r is the discount rate (or risk inherent in actually getting C). Think of r as an interest rate- you demand a higher one if you invest in a risky company.
Throw in growth and it becomes C/(r-g) where g is the growth rate. As you can see, g is very, very important. Valuing a company is much more complex, but the same basic truth holds - growth is a huge contributor to value.