This feature was shown to me this morning for an AllThingsD article with a iBook-bookmark-style icon which when touched(clicked), the exact article (not the Facebook post) is saved. The activity is also added in our Profile Activity but in my case the privacy option was set to ‘Only Me’ by default maybe since it’s a testing-feature.
When asked about the feature Facebook told AllThingsD that, "We’re constantly testing new features, but we have nothing further to share at this time."
Notably, this isn't the first time that Facebook has tested a save for later feature. The site is also reportedly working on a newsreader-like feature.
You can check out some screenshots below...