Yammer is yet another way of pretending to communicate without having to actually communicate.
I for one refuse to believe that you can have any meaningful discussion unless it is face to face. Having found myself on a potential cull list many years ago, I confronted some of the characters in the Star Chamber (after one of them called me to alert me of the fact). Their demeanour told me a lot about where the company was headed. Since that day I have been in CC.
As a team player and a go-the-extra-mile person, this taught me one thing; we can all stand up as individuals against mindless tyranny. When you look someone in the eye and ask them to explain, invariably they will back off.
This company has seriously lost the plot and until we all start communicating again face-to-face, it will only get worse.
FWIW FX