I don't know if this speaks to a generation gap or an experience gap. But if I belong to a generation that "doesn't get" social media, it is not entirely because we're computer illiterates. Many of my classmates have had rockstar careers in the tech industry. I seem to remember that some 40% of Oracle's new employees in 1989 were recent Stanford grads. If anything, we are a bridge generation: the first to use desktops, but prior to the domestication of the Internet.
The experience gap is not inexperience with machines, but is inexperience with their unique kind of social presence and interaction. We're not used to the practice of posting profiles about ourselves (I exclude myself), and of keeping constant contact (in a discontinuous and partial sort of way) with friends and colleagues. We're phone-based and email-based, and at our stage in life, time simply doesn't afford us the surplus attention with which to attach ourselves to the social web.
Time would be the reason most of us would cite for our online invisibility. But I think that there's something more.
For lack of a better phrase, I'll call it the "alienation" of social media. To integrate social media into your daily life you need to project yourself into it. You need to be able to live in a kind of time that's very different from the time of the everyday. You need to be able to pay attention without bankrupting your focus and concentration, need to be able to sustain high levels of availability to a world that's neither "here" nor "there," again, without dissociating from the here and now.
From /Message. This is a must-read about differing generations of web users. By Adrian Chan.