Facebook: Simplifying the Stream
developers.facebook.com
developers.facebook.com
Also this should come with a box up the top with specific help pages written up to explain it all, if people who develop and use web apps every day find it different and confusing, imagine the average facebook user.
I understand that right now I'm a tired and distracted reader (30 hours of flying today and in the airport lounge) but I can't help think that other folks are going to be frustrated by this, even if it's an improvement.
Sites need to be very, very careful about changing stuff that works. This looks like a great improvement, but it you don't get something for nothing -- there is a cost of change.