How can I see the Google Hangouts online status (away, idle, busy, ...) of my friends? I can see the small green line but nothing else when the person is away.
Unfortunately, Google Hangouts does not have the feature. According to googlesystem.blogspot.com, it is actually an upgraded version of Google+ Messenger, not Google Chat or Talk, which is why Hangouts has very little in common with Talk. Hopefully this is in the works, and will be in fixed in future updates. Sorry if this is disappointing news.
However, I just checked one of the Google groups you can get to by clicking the "Relevant" next to Alex's response. One of the people from Google said that it is in the works.