Earlier quoted context omitted.
In my case the personal answer is that there is simply nothing productive, at all, about using Facebook. It is indeed a total waste of time - for everyone. I've yet to see anyone actually get any work done while facebook.com is up on the screen. Perhaps some small businesses use it to communicate with their customers - I don't know, because I personally cannot ever associate Facebook with "service I want to use". Fac…
Facebook had to overcome a pretty steep disadvantage to beet e-mail. The main difference I see is that in e-mail, everything you see (in theory) needs your attention, whereas in facebook, nothing you see needs you attention, but everything is avalable when you want to give your attention. Unlike e-mail, people can join the conversation without an explicit invitation.
But if I check email right now, I can come back and see the same emails that I haven't read yet, a week later, sitting in the same approximate location.
Also, umm .. really, this: "Unlike e-mail, people can join the conversation without an explicit invitation."
.. just doesn't seem quite right. Ever been on a proper listserv?
Actually, your observation - and don't take it wrong, but I think you got it .. not .. quite .. right - is fascinating. You actually have it completely inverted, in my opinion - is this because you learned to use Facebook before you learned to (properly) use email? Not trying to be offensive, but this inversion seems pretty obtuse ..