Before large software companies roll out new features to everyone, they usually do A/B testing to make sure everything is going to work alright and to compare usage statistics.
In my country (Spain) they have been working like a year or so. I think more countries were used to test.
In my limited experience (I don't use much fb) I don't see a lot of people really using it. It's about 80%-likes/20%-the new "emotions" that people use in posts.