as far as i have used iCloud sync documents between my iPad and iPhone, it keeps the file synced on both of my devices (as well as on the cloud) even though if i edit it only on one device it is pushed to the other device as well. i'm sure it is going to work the same way with OS X Lion.
i think if they will add AIM, surely they will add other IM client supports which right now ichat is having. by the way i hate that iMessages doesn't syncs the messages which i get on my iPhone mobile number. i hope they will add that too.