But what of the log in your own eye, I ask? You complain that they never speak to you, but when was the last time you spoke to them? A relationship cannot be one-sided. It takes two to tango, so to speak - it takes two to add one another as friends on facebook (even if someone complains, "but he/she added me!" it is worthwhile to remember that you're the one who still had to click "ok"), and it takes two to keep that friendship active.
Which is why I do not participate in the facebook cull. I have what is known in my inventive parlance as the facebook cycle.
I try, with a reasonable reliability and regularity (in practice, I'm still very bad at this, as I find it does take a significant amount of time), to contact everyone in my facebook friends list. To comment on a great photo from their vacation, to send them a link I think they'll appreciate, to write "Remember the time we...?" on their wall or even just poke them. And the response I get is amazing (because, of course, I have wonderful friends!). I hear hilarious stories, I enjoy fantastic pictures, I'm directed to the funniest and most sincere websites on the internet, and I get to stay in touch with people whom I consider friends. This is really the important point. These people are my friends, and I value that friendship - even on facebook - and so putting in the time and effort to nurture that friendship is important to me. It turns out to be important to my friends as well.
So the next time you're considering a facebook cull, trying contacting those people first. After all, if facebook really is about relationships, it means we're all in this together.