Yammer Cons
Too social, not enough worktools
Low adoption rates ("We have Yammer, nobody uses it")
No on-premise version you can host on your own server
Few customization options
Must pay for SharePoint, Office 365, Lync, Exchange, OneDrive to make it 'usable'
Up to $20/user/month, gets to be pricey very fast
Bias toward Microsoft products 
