I recently set up a Facebook profile. I'm pleasantly surprised by how good it is. They got a lot of little things right, as well as a few big things. Like news feeds.
At signup I did the usual tacky thing of listing twenty or so friends. The next day I logged in and found a bunch of friends requests from people I didn't even know were on Facebook. How did they find me? Via their news feed. They logged in and saw "Your friend Alice Toklas added Nelson Minar as a friend". And so they knew I was on Facebook and they added me, too.
The news feed is the single biggest innovation I've seen in Facebook. It instantly enhances the social network by letting me see things my friends do with their friends. It exposes me to new people and applications. And it gives me something new to do on Facebook every day. Clever.
Interestingly, the news feeds are also the thing that caused a giant privacy kerfuffle when first introduced. Users found it creepy that suddenly their friends were seeing what they're doing. So Facebook added a bunch of privacy options to hide your updates. Of course it all defaults to full openness, which in this case I think is the right thing. It may have been a mistake to foist news feeds on old users without some warning first, but as a new user I love them.