Or, for that matter, any other social networking site, you should read John Brownlee's post about an iPhone app called Girls Around Me: This Creepy App Isn’t Just Stalking Women Without Their Knowledge, It’s A Wake-Up Call About Facebook Privacy.
The post's title says it all!
Charlie Stross expands on Brownlee's story to flesh out the whys and hows of the incentives that drive social networking sites [via Brad DeLong], and their implications for people using those sites:
The problem is this: all social networks run on the principle that if you're not paying for the product, you are the product. They operate as profitable businesses because they encourage users to channel their social interactions via their network, perform data mining on the interests that users disclose, and present the users with advertisements tailored to their interests (which are consequently much more likely to result in a successful sale).
However, to make such micro-targeted advertising practical, the social networks need to motivate their users to disclose information relevant to advertisers. There's no point marketing bacon to Jews or Muslims, so religion is relevant. There's no point marketing turkey to vegans or wheat products to coeliacs, so dietary preferences and medical conditions are relevant. If a user is a member of a subculture associated with a distinctive clothing fashion, that information is relevant to garment vendors. And so on. So Facebook, Orkut, G+ and so on all attempt to induce their users to maximize their self-disclosure and to tie their accounts to as many useful third-party information sources as possible.
You may have noticed that Facebook provides privacy controls, for those who are sufficiently worried about stranger danger to want some illusion of control. Unfortunately the vast majority of people have no idea how widely visible "show to all" really is, or that it might enable the users of apps like "Stalking Targets Around Me" to identify and track them. And it is not in Facebook's commercial interest to promote the use of privacy controls [Emphasis in the original]. If someone is using the privacy controls with all the settings jacked up to 11, it becomes very unlikely that long-lost friends and relatives will be able to make contact with them through Facebook. Which is a lost advertising opportunity, and therefore detrimental to the revenue stream.