I use Facebook. Google+ has two big problems. Firstly, no-one actually uses it. It doesn't matter how great it might be, a social network is completely pointless if your friends aren't using it as well. Facebook worked because there really wasn't any alternative at the time. Sure, there were things like MySpace, but they were all very different in terms of actual functionality. Facebook did certain things people liked, so they'd encourage friends to join up and it grew fairly quickly. But Google+ doesn't really add anything. It might try to do things better, or at least differently, but I'm not about to start duplicating everything on Google when it's already on Facebook. Without adding anything new, it's just a second Facebook without the user base and there's really no incentive for me to join.
The second problem is that Google are pretty much dicks about it. I signed up to Facebook because my friends were using it and it was a convenient place to do things like arrange events and put up photos. I've not once been hassled by Facebook trying to get me to join, or trying to trick me into joining or anything. They just sat back and ran the thing and hoped that it was good enough for people to want to use it. Google, on the other hand, are pretty much trying to force me to sign up at knife point. I've never signed up to Google+, but apparently they've forced me to have an account anyway just because I created an email account a decade ago. I have an app on my phone that not only can't be deleted, but constantly hassles me about updates and other crap. I have a stupid bar on the screen when I try and search the internet that either tries to log me into stuff or just does it automatically. And so on. Google aren't trying to encourage me to sign up, they're constantly harassing me in the hopes I'll give up just to shut them up, and when that fails they're just pretending I've given up and signing me up to everything anyway.
Virgin use similar tactics as well, and I just don't understand how some companies think it's a good idea to piss potential customers off as much as possible. I signed up to broadband with TalkTalk, because at the time they were the best for me on price and pretty much equal to everyone else on speed. In the years since then, I've been getting two or three letters a week from Virgin trying to irritate me into signing up with them. Sometimes they're up front about it, often they try to disguise the letter as something else so I'm forced to actually open it and read it before knowing that I should have just thrown it out.
The thing is, according to independent tests of broadband, Virgin are actually by far the best, and anecdotally they seem to be one of the better ones for customer service. If they'd never sent me a single letter, I'd probably have switched to them by now. But because they've deforested a significant portion of the world for the sole purpose of sending me junk mail, I will never sign up to them even if they offer to pay me for it. It's actually got to the point where I don't even bin their letters any more and instead rip up the contents, put it back in the same envelope and post it back to Virgin without a stamp. Seriously, **** them.
The point being, Google+ could be the most incredible service ever invented, but if I could I'd rip up the internet and post it to Google in small pieces rather than joining. If you want me to use your service, spend your resources on making a good service instead of trying as hard as possible to piss me off.