This morning facebook changed their users' contact information to Facebook addresses. Lovely. So now non-Facebook-users will have their e-mail addresses captured by Facebook if we respond to mails from those addresses. Probably in itself not a big deal. But it's just another example of Facebook knowing they can treat their users with no respect and few of the users will leave.
Another issue is that as people start responding from their Facebook addresses, will others trust that the sender really is who it seems to be? Will people open bogus Facebook accounts to spoof other people? Clearly yes, but that happens with most providers. Again, probably not really a big deal.
Of course, current Facebook users are annoyed because they have to either change the contact info in their profiles back to their preferred e-mail addresses or start checking e-mail in multiple places. Do you really want e-mail between your financial institutions and yourself going through Facebook? I don't think so. Do you really want work-related e-mail going through Facebook? I don't think so.
It'll be a little while before I respond to e-mail from Facebook accounts. Hopefully others will resist this power grab.