Look at the Yammer feature list; microblogging isn't marginalizing email, it is pretending to <i>be</i> email.<p><pre><code> Behind the firewall installation: Yes.
Public notes: Mailing list.
@replies: Reply.
DMs: Standard email.
Groups: Mailing list.
Private groups: Mailing list.
File attachments: Duh.
Favorites (a form of bookmarking): Flag.
Tagging: Filters.
Conversation threading: Standard.
Unlimited character length: Email started this fad!
Search: Duh.
</code></pre>
This begs the question, <i>What the hell is the point?!</i> Email already does email pretty well and is much more familiar to people (especially the old crusty decision makers) so why choose anything else?