Recent quotes:

Jive’s acquisition of StreamOnce continues to lead to new connections, and now, on top of the earlier email integrations of Outlook and Gmail — allowing full participation of email-only users in Jive social interaction — Jive has announced four others:  Dropbox, Chatter, Yammer, and Evernote. Yammer is kind of interesting considering Tony Zingale, the CEO of Jive, declared Yammer “dead” last week.
Yammer and Klout announced a partnership allowing users of Yammer to integrate Klout scores and areas of influence into Yammer profiles.
Microsoft lays out more of the vision for Yammer