Eh, I remember the days of trying to keep in touch via email, and not getting replies, or feeling bad that I wasn't sending a reply. Just to keep in general contact, with no specific goal in mind. I don't look forward to going back to them.

Facebook has become something of a "Third Place," in this respect.

http://en.wikipedia.org/wiki/Third_place

if people don't reply to your emails, maybe that says a lot about how much they care about you.

Exactly? I'm talking about a situation where we both care exactly at a "casual Facebook friend" level. Like we would meet up if we were in the same town at the same time, but we aren't writing emails back and forth about what has happened lately. And that is great, IMHO.

Or maybe it says nothing about that -- but more about their email patterns, work stress, guilt, etc.

Exactly. And if you keep seeing similar posts on a regular basis from the same set of people (close or distant), it gets repetitive and boring. How often do you need to know that x is doing y?

Any of my more "important" relationships are maintained via frequent text messages and less frequent phone calls. For me, Facebook is rarely used for keeping in touch and mostly for its group features. Otherwise its just old acquaintances from yesteryear who'd I don't necessarily care to keep up with anyway. In fact, if it wasn't so painstakingly tedious to delete large numbers of "friends" on there i'd probably only have about 50.