Is there any way for my contacts to know whether I have put them in circle "Close friends" or "Annoying acquaintances" ?
In Facebook, groups can be public. I could not see that directly on Google+, but maybe some APIs have access to it? Or is it something that Google considers as a an important privacy point?
The Circles feature works one-way, meaning that their members can't see if they are part of a Circle or not.
But Circles are one-way, or asymmetric. Everyone sets up their own Circles and nobody knows whose Circle they are in. Secret Circles would be a more apt description. Zuckerberg seems to be suggesting that they are not really groups because instead of everyone in the group knowing who else is in the group, it is the exact opposite: nobody knows which groups they are in.
From here: http://techcrunch.com/2011/07/06/zuckerberg-dig-at-google-circles/
From Google's own page:
When you place people into circles, or when you share with your circles, we won't disclose the titles of the circles people are in. People in circles that you share with may be able to see some of the others with whom that content was also shared.
