I have been using Google+ since nearly the week it launched, and have noticed a few trends that over-familiarity with Facebook and Twitter has brought with it. However, Facebook has recently come out with the ability for people to subscribe to users' public posts without mutually following one another.
I've got friends who have circled me, and I circled them back, but have never seen them post anything publicly. I've got friends who posted things and then asked me if I saw them, only to explain to them I was clearly not in the circle they shared the amusing anecdote with. The average non-tech nerd user of this service thinks it's a Facebook knock off. I stated before that that is its biggest weakness. So that being said, I no longer circle people back on Google+. It's not because I'm a jerk, but because this is NOT Facebook. Nor is it Twitter.
I've noticed two things happen when I started doing this:
1) People are circling me to follow me, but not share anything with me. I love two-way interaction, and socializing, and I've met MANY people from just adding all the suggestions Google+ has given me in the 'find other users' panel. Someone with many followers publicly shared a circle that I was in, and for a day or two I had a huge swarm of people circling me. I would go to many their About pages to see if we had anything in common, or at least to determine what might be the reason they started following me. I just don't have the time to circle back everybody who is following me, especially if I don't know why I should.
2) I had started following people back who are sharing things I'm not interested in, and it's cluttering up my stream. I have a "default" stream I created which allows me to view the posts from the "most interesting posters" circle I created. This is much more manageable, but reciprocating on Google plus is not necessary. If people are only following you in order to have you follow them back, then they are missing the point of "social" networking anyway and are just trying to build a following. I'm an aspiring author, I've got a podcast I want people to listen to. Sure, I'd like to be more 'known', so I understand this, but I don't really have a strategy that involves only getting people to follow me.