G+ at least gives us lots of opportunities to talk about G+.
Google+ Circles don't come anywhere near modelling the complexity of our online interactions.
One of the main topics is Circles, which people seem to have difficulty thinking through - either in creating them or understanding how they work.
This interest in circles is a bit surprising because Facebook has had Friend Lists (which are basically the exact same thing is circles) for a long time but almost no one talks about using Friend Lists.
So I have to give Google kudos for drawing attention to this type of feature, although I'm a bit puzzled why it gets so much attention since Facebook is the same, even to the extent of a per-post pulldown at the bottom where you can select the lists that will see your Facebook post.
Facebook is actually placing more emphasis on Groups now, perhaps because G+ doesn't have groups (yet anyway).
It's important to understand that Circles & Friend Lists are filtering-at-source, outbound filtering, content "channel" preselection. There are two common scenarios for outbound pre-filtering:
1) The "NOT" scenario for personal content, e.g. I want my friends to see this picture but I do NOT want my family seeing it
2) The "I want to signal a topic, content type or urgency" scenario, e.g. I will put these photos in the Ottawa buildings group
First, it's important to understand the "NOT" scenario is a fantasy, it's pseudo-control over your content. Basically as long as the content exists in some recorded, viewable (or hearable) format somewhere, it can be made public. If you want private, I suggest spy-type park bench conversations with a noise screen and check your companion for a wire first. Other than that there is no private. There's only pseudo-private.
So for example you can push content into your "Super Top Secret" Circle with "sharing disabled" on the post, but anyone in that circle can just copy and paste or screen capture or take a photo of the screen or any of dozens of other methods of duplicating recorded content (some more work than others).
(As a side note, this is why DRM is a fantasy, which doesn't stop attempts such as Microsoft's Information Rights Management.)
So putting your content anywhere, whether it be in an SMS, an email, a Facebook posting... you should expect it could become public at any time. This is why I would suggest against say, creating two Google+ Circles called "Circle where I pretend I love (task)" and "Circle where I tell people I trust that I actually hate (task)". That's just asking for trouble.
There are lots of ways people currently use entire sites or communication types as different types of channels.
Sometimes you use a channel to reach a particular group, sometimes you use it because it provides pseudo-privacy, sometimes because it signals urgency or lack thereof. Sometimes something that seems like a very simple channel is actually very complex (the most notable example is Twitter).
For example, I use
* email: rapid ad-hoc bi-drectional "private" communication - also if I want to be sure you will see it (the TCP of messaging)
* SMS (text messaging): realtime 1-1 bi-directional "private" communication; urgent; expectation that message will interrupt someone
* Facebook: either "private" sharing with a group (friends) or sharing-because-it's-where-everyone-is for e.g. work people who don't use other channels - but with no real expectation everyone will see it (the UDP of messaging)
* Yammer: in theory for sharing with closed work group of people just at my department (I say in theory because there is not enough use to see if it works well)
* Twitter: public stuff of interest with no expectation everyone will see it (UDP) plus signals of topics (hashtags) AND signals of per-individual interest (@ someone is public way of signalling, DM says this is both important and "private") AND accounts for different types of audiences (e.g. some people use different accounts for regular tweeting and livetweeting, or different accounts for different topics)
* blog: a mix of long-form ideas (with no expectation they will be read) and link sharing (for people who don't follow other channels)
* Topic or participant-specific groups: many tools (Facebook, LinkedIn etc. etc.) provide this feature where people with a common interest or some other factor in common can have a shared space.
There are channels that I never use, just due to the particular group of people I communicate with and history (e.g. use of instant messaging grew long after I was in the habit of emailing friends).
The short overview above is just to make the point that there is a lot more nuance to "the subtlety and substance of real-world interactions" as Google puts it than just controlling what channel you push into. For work content, public with at-destination filtering (e.g. publish & subscribe) may make more sense as I usually don't know a priori per-individual what content may be of interest, and I'm usually not engaged in pseudo-hiding content from one group or another.
In summary, at the moment Circles only makes sense to me as a way to NOT share content with selected individuals, which is more of a Facebook use case, but be mindful that at best this is just the appearance of not sharing content; it can be copied and made public at any time. The single most notable absence in Google+ is the lack of groups. Since Circles are not just per-source filtering, but fully or partially hidden per-source filtering (you can't see who is in someone else's groups, or even their group names), Circles doesn't help people form interest groups. This is kind of weird since one of the aspects of the Internet is that, far from being the anti-social medium portrayed sometimes in the media, the Internet leads almost naturally, organically, to people forming discussions around common topics of interest. Google does of course have an entire Groups product, called, well, Google Groups, which is an inheritor of the USENET tradition of granular per-topic discussions.
There are a lot of ways that Google could make this experience easier:
* first and foremost Google+ needs to provide Group functionality - just a next-generation version of Google Groups would probably do this
* use GMail data to suggest groups (this technology has already been built by Google, it will suggest possible "missing people" when you compose an email, based on people you usually email together)
- similarly use GReader and GBuzz data
* partner with LinkedIn to suggest groups - either based on connections (see my post LinkedIn maps my connections on LinkedIn clustering) and/or based on existing LinkedIn groups
* extract communication patterns from Twitter to suggest groups, also allow import/conversion of Twitter lists
* alllow various location-based groupings including: location groups based on profile location (or past location) information; location groups based on location detection in browser; location groups based on topic declarations (for example I would like to be able to share information just of local interest to Ottawa residents, but there's no way I'm going through every single person who follows me and figuring out who lives in the Ottawa area)
* allow recipient (destination) filtering by content type and content source, so I can e.g. choose to see all your posted external links but none of your photos or status messages (Facebook provides this to a limited extent and Friendfeed provides this for every separate content source it knows of)
* statistics so you can discover who is using & sharing and "+1ing" your content and can adjust your channel models accordingly
* pull channels (e.g. pull in content from Twitter, perhaps filtered by hashtag)
Ultimately the point is that our interactions are much richer than a flat communication model - but Google has provided only one small aspect, pre-filtering at source, out of a much much larger set of source, topic, and urgency filters. Pre-filtering at source is mainly use for (an illusion of) personal information control, not for work sharing. Google+ does not come anywhere near modelling the way people currently signal public/private, topics and urgency by their choice of channels.
There is a great post that explains this much better than I have above: Dave Gray - Sharing universe.