[Porter_423]

Yammer is a way for mid-sized businesses to make themselves feel cool while undermining their internal data security; in the wrong hands it can undo all the work of a whole world of corporate controls and make company data subject to tampering by anybody's close friend or casual acquaintance.

Having been exposed to 4 different Yammer networks, I can see why most dp pros find it a gross interference with their job and not worthy of inclusion in any real plan for internal communication.