So, it seems that Facebook is testing a new feature to identify topics being discussed in posts. I see a few mentions of it in a Twitter search, but otherwise, nothing about it in any search engine so I don't think it's very widely deployed yet. (see Here is a grouping of posts about iPhones, here is a grouping of posts mentioning Harry Potter, and here, a grouping of posts about lollapalooza)
Here are three posts by friends who mentioned something about Google. Not that Nick's post is only sort-of about Google, and the Google mention comes from the text of the website, not his writing.
Facebook is trying to do some entity recognition - it knows what 'Google' is and provides a suggested page. It's not just straight string matching, because I have multiple friends who have posted something about the S&P downgrade or the recall elections here in Wisconsin, and neither of those got a grouping.
Facebook makes it easy to say "This grouping is wrong", or "This grouping is correct but this item shouldn't be in the grouping"
When Facebook rolled out its OpenGraph work in 2010 and revamped how pages were "Liked", including revamping your individual interests into pages, they imported data from around the web to beef up those new interest pages.
It seems that may at least be a part of what Facebook is using for its entity extraction. For fun, I went to Wikipedia, clicked on 'Random Article' and got 'Floridiscrobs dysbatus' (a small aquatic snail, it turns out), and mentioned it in a post. Now, when I go to the Facebook page for the snail, it knows that I've mentioned it in a post.
If any of your friends mention it, their mentions show up on the page as well. It's fast, too - those mentions show up on the snail page within a few seconds of the posts going live in the news feed.
However, it didn't trigger the 'Grouping' feature in my newsfeed, so I'm not sure what it takes to get things grouped together.
It's entirely possible that 'related posts' is a feature that's been around forever and I've never noticed it before, but if so, it could be getting a whole lot more interesting if the news feed is going to start pushing topics as hubs for discussion.
Facebook is also blessed with having millions of users training it on what groupings are good, and what groupings are bad. That's got to make for some pretty powerful data as time goes by.