In an Internet Week article columnist Cory Doctorow describes how Facebook and other social networks have built-in self-destructs: They make it easy for you to be found by the people you’re looking to avoid.
From the article:

If there was any doubt about Facebook’s lack of qualification to displace the Internet with a benevolent dictatorship/walled garden, it was removed when Facebook unveiled its new advertising campaign. Now, Facebook will allow its advertisers use the profile pictures of Facebook users to advertise their products, without permission or compensation. Even if you’re the kind of person who likes the sound of a benevolent dictatorship this clearly isn’t one.

Many of my colleagues wonder if Facebook can be redeemed by opening up the platform, letting anyone write any app for the service, easily exporting and importing their data, and so on (this is the kind of thing Google is doing with its OpenSocial Alliance). Perhaps if Facebook takes on some of the characteristics that made the Web work — openness, decentralization, standardization — it will become like the Web itself, but with the added pixie dust of “social,” the indefinable characteristic that makes Facebook into pure crack for a significant proportion of Internet users.

The debate about redeeming Facebook starts from the assumption that Facebook is snowballing toward critical mass, the point at which it begins to define “the Internet” for a large slice of the world’s netizens, growing steadily every day. But I think that this is far from a sure thing. Sure, networks generally follow Metcalfe’s Law: “the value of a telecommunications network is proportional to the square of the number of users of the system.” This law is best understood through the analogy of the fax machine: a world with one fax machine has no use for faxes, but every time you add a fax, you square the number of possible send/receive combinations (Alice can fax Bob or Carol or Don; Bob can fax Alice, Carol and Don; Carol can fax Alice, Bob and Don, etc).

But Metcalfe’s law presumes that creating more communications pathways increases the value of the system, and that’s not always true (see Brook’s Law: “Adding manpower to a late software project makes it later”).