Why I don't have a Facebook account.
Seeing as I'm getting fed up of people trying to convince me to get one, or being surprised that I still don't.
The blocker
Facebook may also collect information about you from other sources, such as newspapers, blogs, instant messaging services, and other users of the Facebook service through the operation of the service through the operation of the service (e.g., photo tags) in order to provide you with more useful information and a more personalized experience.
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We may use information about you that we collect from other sources, including but not limited to newspapers and Internet sources such as blogs, instant messaging services, Facebook Platform developers and other users of Facebook, to supplement your profile.
- Facebook Privacy Policy, viewed 11 Jan 2008.
In order to sign up for a Facebook account, I need to agree to this policy.
I do not.
I am well aware that individuals are capable of sticking my name (or nickname) into Google and getting back various information about me. In general, I provided that information. I'm pretty certain that I'm also happy for people to generally have access to it, as I've pretty much always been mindful that the Intarwebs are a public forum with a very, very long memory.
However, I do not grant legal permission for organisations to go data-mining, even if they're going to claim it's for my own good. When it comes to entities that have to actually worry about data protection, they're going to have to damn well ask explicit permission for every little morsel they want about me, no matter how much inane fluff it may be. (This is why the "so use a fake name" argument doesn't work. I'd still be giving them a permission I refuse to grant.)
(I am aware that the latter quote continues where such information is used, we generally allow you to specify in your privacy settings that you do not want this to be done or to take other actions that limit the connection of this information to your profile (e.g., removing photo tag links). But I draw your attention to i) "generally" and ii) "limit".)
And, no, I am not going to "just trust them", as their track record is crap.
Contributory factors
They're another blasted closed system. LiveJournal, by contrast, and for all its ills, at least makes efforts to play nice with interacting with other systems-OpenID, RSS, all that kind of stuff. It's not Semantic Web, and it's not open hypermedia, but it's better than "come and be locked into our proprietary system".
So that's why. Prove me wrong, or stop expecting me to know what you announced over there.