Ranked in these QuestionsQuestion Ranking
Pro User interface is modelled after Facebook
To make it easier to learn for new users and increase adoption.
Pro A complete social network for business
Yammer works like a typical social network with status updates, comments, file sharing, groups, etc.
Pro Hashtag support
Hashtags help organize projects and parts of projects easily. Great for getting an overview of a specific subject and seeing if something's missed.