I think people have very different standards as far as social networking goes. I would recommend deciding from the offset what you want to use Facebook for, and establish friending policies on that basis. If it's for keeping in touch with your nearest and dearest, keep it to a select few. If you want a conduit for talking to everyone you've ever met, add everyone you meet.
If I see someone who only has a handful of FB friends, I assume they're towards the more private end of the spectrum rather than thinking they're somehow socially retarded. Likewise if someone has 800+ FB friends, I don't think they regularly hang out with them all.
There is such a thing as a late adopter advantage. I don't think most people make these kinds of decisions when they first enter into that kind of environment, so you actually have the benefit of deciding off the bat how you want to use it, and how to optimise your usage for that aim.
For people I actually care about, I have better means of staying in touch. My inner circle has had a private voice chat server for years now, and that's part of the reason I haven't really been forced to use a social networking website.
But I'm trying to dramatically change who I am as a person, and this is a necessary step. I have severe issues with self-consciousness and social anxiety (despite acknowledging that this is unjustified as I am affable and attractive) so I am generally looking for ways to ease myself into social normalcy.
I am beginning to suspect that it is surprisingly common for intelligent, competent adults to somehow make it through the world for a few decades while missing some ordinary skill, like mailing a physical letter, folding a fitted sheet, depositing a check, or reading a bus schedule. Since these tasks are often presented atomically - or, worse, embedded implicitly into other instructions - and it is often possible to get around the need for them, this ignorance is not self-correcting. One can Google "how to deposit a check" and similar phrases, but the sorts of instructions that crop up are often misleading, rely on entangled and potentially similarly-deficient knowledge to be understandable, or are not so much instructions as they are tips and tricks and warnings for people who already know the basic procedure. Asking other people is more effective because they can respond to requests for clarification (and physically pointing at stuff is useful too), but embarrassing, since lacking these skills as an adult is stigmatized. (They are rarely even considered skills by people who have had them for a while.)
This seems like a bad situation. And - if I am correct and gaps like these are common - then it is something of a collective action problem to handle gap-filling without undue social drama. Supposedly, we're good at collective action problems, us rationalists, right? So I propose a thread for the purpose here, with the stipulation that all replies to gap announcements are to be constructive attempts at conveying the relevant procedural knowledge. No asking "how did you manage to be X years old without knowing that?" - if the gap-haver wishes to volunteer the information, that is fine, but asking is to be considered poor form.
(And yes, I have one. It's this: how in the world do people go about the supposedly atomic action of investing in the stock market? Here I am, sitting at my computer, and suppose I want a share of Apple - there isn't a button that says "Buy Our Stock" on their website. There goes my one idea. Where do I go and what do I do there?)