Yammer is a type of “social network” specifically aimed at businesses. This is immediately obvious in that you need an email address from your organization’s domain to join it’s yammer network. Yammer has similar functionality to other social networks and you create posts, known as Yams, with hashtags. You can use groups to filter conversations by topic. You can also create external networks and invite third parties to join your conversations.
Microsoft bought Yammer last year for $1.2 billion and added Yammer to the office group and it looks like it will be integrated across all the core products. In fact you can now integrate Yammer with the online version of Dynamics CRM using a simple configuration option. A few things to be aware of the first being that you once you link Dynamics to Yammer it cannot be removed! You also need the enterprise version of Yammer which is a minimum of 5 licenses. Once installed the Dynamics activity feeds will be replaced by your Yammer feed. More details here http://msdn.microsoft.com/en-us/library/jj945277.aspx
Under administration select the Yammer configuration option as shown
Once selected simply add your Yammer connection details.