Take a look at this screenshot taken from a client's post insights screen:
This just turned up on one of the more higher reaching posts for the previous week, so I'm not sure how many people have actually had a chance to see that there is a post to react to, but I tracked it down and without disclosing my client (due to privacy issues), here is what it looks like from the timeline:
As you can see, there are no reaction buttons to click so I was unclear how this would look from someone's perspective (not my own). A quick search on Facebook revealed that users in Ireland and Spain are the only users who will be able to see these reaction buttons. I'll have to check with a former client of mine who is currently in Ireland to see if he can send me a screenshot. :) Stay tuned!
Facebook's information on this can be found here- http://newsroom.fb.com/news/2015/10/news-feed-fyi-how-the-reactions-test-will-impact-ranking/
The overall feedback on mentions has been nothing short of brutal, with both Mashable and NPR among some of the many reporting on the overall negative reactions of users. Page mangers like myself, however, will find the added input highly enjoyable with a hot cup of coffee in the morning.
The complete list of all the reactions? Here is a handy image from Facebook: