Yours truly in August of last year on The plusses and minuses of Google+ - filed under minuses:
For any social networking service the single biggest reason they fail is lack of adoption. While Google has become the fastest growing site of-all-time that doesn’t mean that people are using it. In my Circles (get it?) Google+ has not yet been fully adopted. The people that have been most active are very early adopters, people that work at Google, and people that do not have accounts on Twitter or Facebook. Will this change? Will Google somehow convince people, as they did me, to use Google for a few days to see if it sticks? We’ll see.
It is now nearly 10-months later. How is Google+ doing? Not so well from my chair. They haven't figured out a way, besides Circles, to differentiate themselves from Facebook, Twitter, LinkedIn, and other social networks that clearly have carved out their niche.
I think Google is a great product. It does a lot of things and does them fairly well (although their iPhone application is pretty unusable). If it was launched in February 2004 at the same moment Facebook was launched it would have given the now 900 million user network a run for its money.
So what's the problem? Again, me, nearly 10 months ago:
Every social networking site was started with a particular purpose in mind. Over time those services typically find their niche (if they survive long enough to do so) whether or not it was the original reason for its inception or not.
Google , however, goes against this “find the niche” convention. Rather than trying to fill a niche like Facebook or LinkedIn they’re taking on every level of human connection; professional, familial, social, voyeur, etc. and combining them all into one service. They do all of this by providing a different relationship model called Circles.
At the time I thought this approach would have a positive effect for Google+ . I thought that nearly anyone could find a way to make Google useful. But it seems like it has been the opposite. Perhaps this lack of focus has made it so that Google doesn't identify with very many people.
The only types of people that I see using Google on a regular basis are early adopter tech geeks, social media experts, and people that work at Google. Perhaps someday they'll separate themselves from the pack somehow but until then it doesn't seem like Google+ has caught on with any particular crowd in any meaningful way.