I've stopped using Facebook and behold - all my best friends are still here. If a friendship can't exist without Facebook, then they probably aren't your friend at all...
People do use email still... But pretending facebook doesn't offer any value is an exercise in reality distortion.
It's the complete opposite of email where I think "I'll wait until I have something proper to say" and then never send anything. On FB, it's totally normal to leave one-line comments. Having said this, I barely use FB anymore (due to privacy concerns).
Edit: I should also add that I've never used email in the social way that people seem to refer to. I really don't understand how that would be possible. FB allowed new types of social exchanges that didn't exist before (for me, at least).
An email (whether direct or via a mailing list) is an interruption (at least to me), whereas a Facebook post just drops off the bottom of the page if I ignore it.
EDIT: Sorry, that was poorly worded.
The discovery side of it is more like an RSS reader (or maybe a group email). But the key distinction (for me at least) is that I can be totally passive - I don't even need to mark things as read - or I can engage.
10+ years ago I knew a bunch of people who had personal blogs, but of course most of them were filled with "sorry for the lack of posts recently" type posts.
I'm not on Facebook, but I understand why it's popular. The more people who might be reading, the more reason there is to post stuff. So it makes sense that everyone winds up in the same network.
Someone on the other side of the world posts a photo of something they've been doing, I comment on it and we have a conversation.
For this to happen without the likes of Facebook, they would have to explicitly share that photo with me, something that may or may not be likely depending upon what the photo is about, what their perception of my interests are and whether they think I want to be bothered with it.
Email is a very explicit share. You are telling someone to look at this, because you sent it to them. This is much more personal. There's a social stigma in over-emailing, as much as there is a social stigma in not reading the emails a friend sends you. Emailing pictures is more like calling a friend. Yeah it's nice to hear their voice directly, but what if they don't want to hear what you have to say at this moment?
There are certainly different social assumptions between email and Facebook, but the differences have long started to blur, depending on what context we're talking about (e.g work vs friends, etc.)
I do get the idea, sometimes I feel a little bit excluded without an FB account, but I have never had the problem that somebody didn't have an email address. Not even kids.
People seem to make up all sorts of excuses, but in the end it always boils down to 1) suffering minor inconveniences and 2) the (often[1] irrational) fear of social exile.
As other people have pointed out, changing networks is not that hard. It's a false belief that it is. Years ago my local friends were mostly on MSN[2], East European/Middle East folks were on ICQ and Y!C, US people were using AIM. So I used Trillian and later Pidgin. What you saw was this, people are moving around all the time, and many of the persons were 2 or 3x in my contact list because they too were on multiple networks. Google chat just sort of edged itself in there as well.
Think of it like this, remember how easy it was to find all your friends on FB because of that network? And didn't the same happen with email, and with AIM/MSN/iCQ/etc? I see friends and acquaintances trickle in on G+ without any effort for that reason (except I don't want to use G+ either). Now FB pushes its "help" quite aggressively, but even without that, people connect in networks, point eachother to their friends, it's very peer-to-peer :)
[0] I mean, it happens ... http://www.ibiblio.org/harris/500milemail.html
[1] note I'm not saying "always", I can imagine certain high school scenarios where this fear might be somewhat real, although one has to wonder ...
[2] unfortunately I lost my MSN acct because the not-hotmail domain I registered it to expired a long long time ago and it stopped working--if anyone knows a solution to that I'd love to hear it because I would love to see that old contact list back :) (however I could also reg a new account and repopulate my contacts via-via just as easy)
>facebook has been replacing those short messages that email or IM used to be used for.
I don't get why it's necessary to justify not using such a "tool".
That was my experience a year or two ago. At some point I deleted my facebook account, because the value I got out of it wasn't sufficient to tolerate all those annoyances: changing email notifications, constantly changing privacy settings and policies, annoying ads, annoying messages from people I barely know...
Mind you, the constantly shifting privacy settings are weird, its easy to be really granular (go to your Activity Log) but it is effort. You can also change privacy on a post by post basis, but its sticky, so you need to be careful. The ads never really bothered me (except for the dating ones just after i came out of a long term relationship). In fact, I never ad-blocked facebook because I could x out of ads I didn't want to see. The annoying messages from people is not really Facebook's fault, though I feel your pain....
Even now there are still simpletons who don't understand the reasoning of those deciding to stay away of these sites. I'm saying just understanding it, not necessarily agreeing to it.
Making someone into an outcast because they do not use your favorite social networking system is the problem here.