The general repsonse to the Circle system within Google+ has been positive but there is an underlying worry that they may not work. Whether because it is a departure from behaviour on other networks where lists and groups seem to have failed, or because they may not be sustainable when the number of friends becomes larger the concern is there.
Dave Winer posted that Google+ Circles are bound to fail because it is human nature to start with the best intentions when organising and categorising our data and friends but, after a while, we become lax and this falls by the wayside. This may well be the case elsewhere but Google+ has a key difference: you are made to add a new friend to a Circle when you start following them. This is the way you follow people rather than being an afterthought.
Admittedly, people could cop out and just put all their friends in the "Following" circle but being made to think about that choice at the very beginning makes us far more likely to stick with it on Plus.
Sarah Perez over at ReadWriteWeb argues that Circles may not be sustainable because of the numbers involved and because our relationships with those we follow may change necessitating a re-ordering so that everyone sees what they are supposed to see.
AJ Kohn has written an excellent, extensive look at Plus and warns of the dangers of excessive "friending" due to the simplicity of the system and that Circles may not be a "best fit" for reading (rather than sharing) because of the multiple interests of those involved.
The argument that we are more likely to follow more people and may have to resort to a "people I don't care about" Circle is made redundant by the incoming stream. Following is asynchronous by design and we can utilise the incoming stream to vet people sharing with us before even considering whether we should add them to a circle. This is a master-stroke by Google in my opinion and sets Plus apart from other networks in this regard.
Some may say that, within a week of being on Plus, they are already following more people than they have during years spent on other networks. Is this just as a result of a clever, easy to use system? Are we so shallow that Circles has encouraged us to abandon our previous behavior? Probably not.
Perhaps people are following more as the engagement is better and not out of an uncontrolled urge to use the pretty circles. The current lack of aggregation in Plus (who knows if it will stay that way) means that all shares are explicitly intended for the Plus audience and the quality of those shares is generally better as a result.
Twitter has a nice simple single click system, you just hit that follow button - no circles to worry about and no decisions as to where you want to place people in your friending hierarchy, but we dont get out of control. If it is too easy to follow people on Plus then, by extension, we should all be following thousands on Twitter but the reality is nothing like that.
We are currently in the "shiney new toy" stage (and what a toy it is) during which we generally see a high volume of interaction as the early adopters push the boundaries in order to discover what the service is capable of, what it can't do and where the bugs are.
Early adopters are, by our very nature, outgoing and vocal. We are often media types, bloggers or social media big hitters with a narcissistic streak - it is no surprise that we see an initial explosion on a service such as Google+. We generally make a lot of connections but, as AJ says, we are not the normal user - what may work or not work for us will not apply to those who join in the long tail.
Once the doors are open to all I would doubt that Joe Public would act even remotely like your average early adopter.
Content is King
Circles alone are not the answer to an effective network. The old blogging mantra says that "Content is King" and this is equally the case on a service which is all about sharing.
AJ Kohn is correct when he says that conversation happens around pieces of content, or social objects. These social objects become the online equivalent of topics discussed during water-cooler moments - connecting us, giving us something in common, something to share even if only for a short period before going our separate ways. This is why Sparks needs to improve (and fast), topic filtering needs to be greatly improved and our options for sharing to Plus need to be extended.
This does not mean that G+ needs to enable content aggregation but a bookmarklet to "Share on Google+" is a step in the right direction so that we can be away from the service but still share content - a more natural experience. Android users already benefit from an extended sharing model due to the extension created by the native application and Places check-ins from Google Maps but, for others, we need something for those without an app who call the browser home.
Implicit v explicit
Although Circles appear more flexible than options on other networks they do still fall in to the trap of being explicit groupings when the world doesn't always work like that. As I mentioned previously we drift in and out of implicit social circles throughout our day without even realising it.
Plus is designed to better reflect our offline behaviour but Google needs to find a way to take advantage of implicit connections based around social objects - temporary topic based circles - that may be completely unrelated to our existing friends lists.
While it is currently very easy to find people, subject discovery will only thrive once full search is implemented and Sparks has a bigger (and better) data source to pull from.
I believe that we should also not be limited to sharing a topic with our circles but should have a option to share our thoughts with others talking about the same thing - perhaps a temporary circle "who is talking about x". This could be the basis for some kind of trending topics architecture or merely a way of advertising that you want to talk to others about your given subject - Plus could then hook you up with others or show you existing threads related to your topic of choice.
Maybe we could find people based on their sharing patterns, +1's or interests in their profile. We may currently be able to search Twitter for our interests but there is then no direct link to any discussion about that topic - Plus could immediately step in and fill that gap.
We must avoid getting completely hung up on circles - they are not the Holy Grail of social but a workable solution to a particular problem. We must refrain from trying to modify our behaviour to fit a problem which, for the most part, does not exist. Circles are a useful way to restrict the visibility of data to a select group whilst publishing it in the same location as everything else thus avoiding the need to use multiple platforms - just as with the way I argued Blogger could operate if integrated deeply in to Plus.
Most of what we share in our day-to-day use of social networks is very general in nature and is therefore best suited to being shared publicly. We have the flexibility of Circles but do not need to constantly use them.
Whilst we ourselves are keen to have better discovery, so are others. If everyone were to share to just their Circles then all we would see on our profiles are blank Posts tabs - hardly conducive to good discovery and communication; we would have no incentive to follow anyone as we would be unable to see the type of content they enjoy.
There must be a balance
We may not be using Circles 90% of the time but they offer us choice, they offer us that flexibility and they offer us an element of control which we can use when we need it.