Facebook has made some interesting attention economy moves over the past few months.
Last November they created a new feed  called "Pages Feed". It seems to be a chronological list of Pages I'm "connected to" . It's somewhat hidden; I'm sure most users will never see it.
Since then  Facebook has changed the algorithm for what appears in my "News Feed" . If I sort chronologically ("Most Recent") , I see it includes all the "Page Feed" posts, but if I use the default "Top Stories" ranking many Page Feed posts disappear down the screen. Some are still near the top, but some are so far down I'll never see them.
These two changes are related. Unless Page owners pay up , their subscribers may not see Page Posts ...
... Promoted posts appear higher in news feed, so there's a better chance your audience will see them...
It's not clear if user interactions with a Page post (like, comment, share) still change the ranking of future posts from the same source ...
Posting works the same way it did before. When you share a post it gets delivered to the audience you specify.
If someone you shared with didn't notice your post it's likely because they:
... Didn't scroll down to where your post appeared in their news feed...
My internal lawyer looks at this and thinks "It all depends what you mean by the word works". The Post does get "delivered", it just won't be "seen".
My hunch is that, for the moment, Page engagement still matters. That is, if you interact with a Page post (Like, Comment, Share) you will see similar posts in the future. If you don't interact however, you'll only see them if the Page Owner pays or if you are the .1% who will notice the Pages Feed.
From my perspective, this is a dual bummer. As a Page subscriber If I didn't want to see Page posts, I'd unsubscribe. Facebook's ranking algorithm is simply an annoyance -- not to mention I prefer the deprecated "Most Recent" sort order. As a Page owner this means my sports teams, clubs and groups are missing news they care about -- like a change in practice schedule.
From a business perspective, assuming interactions still affect sort order, Facebook can win two ways. If Page owners pay then Facebook gets money for placement, if consumers interact more then Facebook learns more about customer interests.
On the other hand this change makes Facebook less useful for its customers. It opens up opportunities for Google if they could, you know, stop shooting their tentacles off. 
- fn -
 Facebook, for me, is the commercialization of RSS pub/sub post/feed technology. There are three active feeds - Pages (new), News (Page Owner and Profile activity), and Unnamed Right Side -- Profile detailed Page/Profile activity sorted chronologically. Incidentally, Pages still have RSS feeds, and Profiles used to have them but that was removed 1-2 years ago.
 Subscribed to Via the "Like" action.
 Page and Profile feeds I subscribed too via "Like".
 This is increasingly hard to do. Facebook will periodically revert sort order to their algorithm-generated "Top Stories". I'm not sure "Most Recent" even exists in the mobile app any more. I expect Facebook to remove it altogether.
 Google Reader is (again) rumored to be facing imminent execution. If Google had embraced standards-based pub/sub for G+ instead of killing off RSS (and Reader Shares) the world would be a different today.
 In theory the Promoted Page option dates back to Oct 2012. In practice it's been quite subtle until recently, and I think the algorithm changes are newer. Facebook has figured out how to make big changes in an incremental fashion.