So if I post a direct message to someone on G+ it should also show up in my hangouts feed?
No - the Google+ messaging service (which sits on the right) now has equal functionality to GTalk/Messenger - this wasn't the case before. They also added functionality ontop of this.
Before in Google+ there was Google Talk, essentially with some added functionality (video chat+). A little while ago they added this video chat functionality to the Gmail chat, so those two services were essentially on par. But Messenger on Google+ mobile had more functionality, and was completely separate from these two chats still. So they basically took the best from all the chars, threw it into one service, added a few features and called it "hangouts".
It's not as dramatic as I'd liked - SMS would make it for me. But that's coming.