- an alert when posting publicly or to one's extended circles that reads "When you share publicly, [or 'when you share to your extended circles'] people you haven’t added to your circles will be able to view your post and may be able to comment."
- the barring of people not in your circles from contacting you (by default)
- a safeguard against talking to unwelcome strangers in hangouts: when someone not in your circles joins a hangout that you are in, you are pulled out of said hangout and, after being notified that [person's name] has just joined, you are given the option to rejoin.
That safeguard has and will continue to spark confusion, due to the language of the prompt ("Your microphone and camera have been muted because [person's name] joined this hangout but isn't in your circles") and due to the word choice, lack of context and downright misinformation by certain tech news sites. (UPDATE 1-29-12: The report from the The Next Web falls in the "downright misinformation" category, along with that of Mashable and PCMag. I apologize for my iffy linkage.)
For those confused, here's how the hangouts safety mechanism works; where I am at all not completely 100% positive, I have used the method of safe assumption:
Bob is a teen. Bob is chatting with his friends, who are in his circles. Another person joins; that person is not in his circles. Bob gets notified that a person has just joined who is not in his circles. While Bob is getting notified, he is disconnected from the hangout entirely: he can not see or hear the other participants in the hangout and they cannot see or hear him. If he, for whatever reason, decides that it would be best to leave, he is given the option to do so, alongside the option to rejoin the hangout; if he chooses the latter option, the other participants will again be able to see and hear him, and he will be able to see and hear them.
The person joining might be a true stranger, creepiness and all, or he could be a friend of a friend. If the latter is the case, it would be rather inconvenient if said stranger was not allowed to join period. Bob would just have to friend the friend of a friend. Did I say friend? I meant "circle."
I don't think the hangouts safeguard is unfair to teenagers, nor do I think it will be much of a hassle for them; presumably public hangouts (like the one the President is holding on Monday) will play by different rules, as those hangouts are likely to have strangers joining them frequently.
In conjunction with today's announcement, Google launched the Google+ Safety Center to help parents and teens navigate through the safety issues that go hand in hand with social networking and to discover the safety features that Google has to offer.