Whereas some people I know have twitter and very few use it regularly, I have never even met someone who has a G+ and very few people I know would even recognize it as a social network over a simple rebranding of their gmail account.
If you want to give feedback, join the 'social network'.
(That's especially fun if applications, even 'paid' applications, try to 'encourage' you to rate in the Play Store. "Look, Yatse. I love what you are doing. But I CANNOT rate you. Firefox? You guys are my heroes. But I CANNOT rate you.".)
G+ is not a failed social network, it's no network and certainly not social. It's a constant slap in the face.
But here's the thing: I have a Google account. Otherwise I wouldn't be able to put down cash in the damn Play Store¹. Just recently I bought a couple of $10 apps. They take my money. They know who I am. I cannot rate any application.
Because my 'Google Account' isn't good enough for that, I need that 'social stuff'. Which I cannot, because my G+ account (I gave it a try, didn't like it all that much and got nymbanned²) is ~dead~.
That's actually like Amazon requiring an account to order things (fine, 'normal'), but you have to connect Facebook to post a review. In one word: Insane. Or broken.
①: Now that is a moronic name and never gets better.
②: I used to change my name from my ~real name~ to 'Ben .'. Account locked out and lots of things are broken. Of course, a while later they changed their minds and now ~real names~ are optional and if you don't want to give a last name they suggest that you use .. '.'. I wish I was making this up.