Historically, shifts in enterprise communication happen every 20 years, and with the millennial generation, this shift will be from email to activity streams.
As a 'millenial', for actual business communication, I strongly prefer email.
I think as long as you have separate streams, they can be much more powerful and useful than email. Think about github and trac. Both have a type of stream to condense information that would be too much for email. Obviously, no one wants to actually integrate facebook with their business communications.
As a 'millenial', for actual business communication, I strongly prefer email.