Something seems a bit...wrong...with Google+'s circles.
Maybe it's just me, but there seem to be at least three different use cases for circles. Some seem to work, others...not so much.
Let's look at the most obvious case--limiting who can see what I post Let's say I have some pictures of my kids, and I want to share them with my family, but not with the internet as a whole. Well, with circles, I can simply post them to my family circle. No problem.
This seems to be the most natural use for circles, and (not surprisingly) it works very well. Unfortunately, it is also the use case that I'm the least interested in. Maybe Twitter has trained me to dance naked in public--but I rarely see the point in limiting my posts. If someone's interested in what I have to say, then the last thing I want to do is put obstacles in their way.
In the second case, I can use circles to send posts to just those people who might be interested in it. For example, I'm a big fan of pen and paper roleplaying games. I'm also very active in a Shotokan Karate dojo. The people in my Karate circle probably aren't interested in my review of the Dresden Files RPG. Likewise, people in my RPG circle probably don't want to hear about my brown belt test. Again circles come to the rescue. I just send the post to the relevant circle.
There is a subtle difference between this and the first case. In the first example, I'm deliberately trying to limit who can see my post. In the second, I'm trying to filter my posts. I'm not trying to limit anyone's access--I'm just trying to make sure that the information gets to the people who may be interested.
Now sounds nice, and I've seen Google's promotional material promoting this use. But it has two problems. First, there's no way to distinguish between "only show these people" and "focus on these people." Google will, wisely, always assume the former. So, if I send a post to my Karate circle, I am effectively limiting it to just that circle. They cannot turn around and share it with other karate enthusiasts. Other people on the net won't be able to search for and find it. And this is obviously not what I want.
Second, this sort of filtering is just all backwards. Say I know George is an iOS Developer--so I add him to my iOS Developer's circle. Now, I don't really know him that well. He may also be interested in my RPG posts, or my Karate posts. Or, and let's be realistic here, he's probably not even following me at all. The point is, George should be able to filter what he sees from me--I shouldn't try to filter things for him.
Which brings us to the last use case for circles. I can use them to filter the information I see in my stream. This sort of works. I put all the tech pundits that I follow into a Tech circle. Then I can look at just the posts from that circle.
Unfortunately, few of us post about just one topic. When I follow someone I get all their public posts. Yes, they may talk about technology a lot--but I also get all the baby photos, birthday wishes, and comments about where they went to dinner last night. Everything. So, as far as working as a filter goes, circles are a crude and very course grained.
The end result is that I have to be careful about the number of people I follow--just to keep my stream manageable. I do organize the people I follow into circles--but then I rarely do anything with these circles. Unless there's a very good reason, everything I post is public.
Bottom line, I don't think circles are really doing their job--at least, not for me.