Mobile Yammer for Everyone
Yammer, of course, has it's own iOS, Android and Windows Phone mobile apps, but now it's going to allow developers to take advantage of some the core Yammer capabilities for their own apps, a move that could spark more interest in the system.
Opening up any system to developers is always a gamble, because developers are always going to want to have access to as much of the core system as they can get, and the Yammer team has to balance that with its own interests.
Open source SDKs are available for iOS and Windows Phone developers, and social business apps integrating the Yammer timeline should start popping up soon. Adding authentication and functionality to mobile apps will allow developers to use an OAuth 2 token to read and write to the Yammer API.
Apps will allow people to sign in with their Yammer credentials, and after authorizing the app, send people right into the main app.
Social Business Mobility
Microsoft has leaned more and more heavily on Yammer for social business, and it's even taking over as the go to newsfeed in SharePoint. Eventually, it will be the default social layer there and in Office 365, Dynamics and other places. How deep Yammer mobile apps will be able to go in that regard isn't known yet, but the potential does seem high.
Particularly in the case of SharePoint, the potential seems highest. There are so many on premise SharePoint deployments out there, Yammer mobile app integration could really prove useful to those teams. It remains to be seen exactly how much demand there might be out there for that kind of configuration, but Microsoft is likely hopeful there will be plenty.