Messaging - email, fb, linkedin, etc
Broadcasting - twitter, fb wall, rss, etc
Instant Messaging - skype, irc, etc
Calling - skype, phone, etc
In Person
That people are doing more messaging through fb, linkedin etc doesn't change that what they are doing is essentially email.
FB - how much ever they make it look like email and function in a compatible manner, I don't think its used the same way email is(talking user behavior). It is just an asynchronous text messaging system. It is closer to chat/IM than to email in the way it is used. FB's bid to make it email-like seems to be an effort to move more of your messaging to FB or have the "unified inbox".
Is it really tough to imagine that 10 years from now we won't use "email" for more than 5% of our communication? And that subsequent generations will probably not use it at all?