http://android-developers.blogspot.ca/2013/12/new-tools-to-take-your-games-to-next.html
The second part of their blog post talks about and links to their Github repository for the Play Game Services Unity plugin.
https://github.com/playgameservices/play-games-plugin-for-unity
Looks real easy to use, achievements, leader-boards, save game syncing, etc… They also support iOS too in the same plugin, they integrate as much as they can with the Unity Social features so that you don’t have to write different code for Android and iOS. There are some extras for the parts Unity doesn’t have an equivalent for though if you want to use them.