I only have two reasons to love Yammer:
1) I love Yammer because it’s easy to use (just like Facebook). To me, Yammer is Facebook on diet …I mean there is no fluff or information overload and you can be much more focused on the conversation itself. Conversations are like the oxygen for my daily work, so I do everything to improve them. Yammer is giving me the oxygen!
2) I love Yammer because it helps me explain SharePoint social features to my customers a lot easier than My Sites in SharePoint itself. Here is an example of how I educate my customers on social features in Yammer before letting them touch MySite in SharePoint:
Have I replaced my Outlook and Lync with Yammer? Absolutely No! Yammer is yet another right tool for the job. Depending how urgent or braod my conversations are with my customers I use different tools. The following picture shows the model I follow: