But even with all that I am fairly confident that Google+ will fail to take off just like many of Google products lately. All they have introduced is a small set of features that facebook lacks. FB can add those in a matter of few months and then take out the whole reason for users to switch. Social networks are very very sticky.
I have to disagree with this. Remember Friendster and MySpace?
That said, it's surprising how few people, even tech savvy ones seem to know about the functionality even though it's been around for ages. In fact, FB used to have a "how do you know this person" question when you added a friend, and they confirmed the relationship when they accepted, which is gone. It could be that they believe that most users don't want to segment their friends by categorizing them.
I wouldn't assume that it's so easy for Facebook to make fundamental changes to their friend system. It's woven into every other part of the site. The whole visibility thing would probably be a nightmare to implement.
Extra feature - no breakage.