The Facebook Open Stream API
developers.facebook.com
developers.facebook.com
Viewing the stream was the last "feature" that was controlled entirely by Facebook, and is one of the primary reasons people come back to visit facebook.com. With this move, Facebook moves away from being a website and towards being a pure infrastructure/platform play; they own the social graph and they are the platform for pushing information through it.
I have always thought that Twitter wouldn't stand a chance if Facebook moved in this direction. Twitter has surprised everyone recently with their growth, but their survival is now hinged primarily on their great publicity rather than any fundamental strategic position. A lot of people still perceive them as a primary force in asymmetric 1-to-many communication, but in fact Facebook is taking this territory with public profiles and pages. Most Facebook pages have at least as many followers as their Twitter counterparts, and these pages can now publish into the stream the same way Twitter can.
Now if only people would build useful stuff on the Facebook platform instead of a bunch of spammy crap.
On the one hand there are downsides and risks being tied to a platform, but on the other hand there are huge opportunities. For applications that are inherently social or have a strong social component, it's going to be very valuable or necessary to live on the social graph. Until now, those companies have had to try to build their own, which is very difficult or impossible.
For now a lot of developers just see Facebook as a way to spread virally, which has led to a lot of annoying spam machines.
EDIT: I was right, there is a new "Subscribe to John" link on profiles today.
"Fans" has way too much weight to it. "People you follow" and "followers" is actually a very straightforward description of the relationship on twitter. Facebook should change their terminology. This is a case of legacy hurting ideal design. They've had "fans" for some time.
It'd be really interesting to see numbers, but I'd bet usage on facebook has gone up massively since their redesign and new emphasis on the 'stream'.
It's funny, because when the redesign went live, about 90% of my friends where bitching about how they 'hated' the new design. Now they're the most active people on my list.
The problem is, Facebook can probably never do this. Most people have their profiles quarantined off. If for some reason facebook ever over-rode those settings and made their stuff public, a true public outcry would occur.
If facebook somehow DOES open full search capability like twitter search/open public timeline, then wow, we're in for something entirely new. The data there and possibilities make me feel like a kid in a candy store.