Hmmm ... Now, I have used my Google account for various things, including submitting a couple edits to Maps etc...
But I've still answered "no" up above. Because I don't actively "use" the core social network bit of G+ (and in fact I don't think I actually KNOW anyone who does, either).
It's sort of like having already been a user of some other services (say, an equivalent to Youtube and to GMaps, as well as buying a smartphone) and finding that a free Facebook or Twitter identity came with, and logging in using that ID was now a prerequisite of using those other services. Well, OK, yeah... I log into this ersatz IP-VoD service with a supposed FB account, or into the mapping site using a Twitter one, but it doesn't necessarily mean that I ever actually log inon FB or Twitter themselves to use their core function of interacting with other people I know and/or share interests with in a meaningful way. It's just a passkey, yknow?
Thus, I have a G+ identity, and I use it for things, as it's been pretty much forced upon me (and in fact, it's now trying to force me to change my display name - uh, sorry, but if "Tahrey" by itself wasn't acceptable, why the titting hell did you let me set my handle as that in the first place? The originally behind-the-scenes surname you now want me to globally exhibit is just a bit of keyspam I entered to make the red outline disappear...) ...but I don't "use Google Plus".