So far, the main distinction there I've noted is the intuitive interface relative to how information or posts are shared. Facebook's main complaint (at least of people willing to stay on it and use it) is the arduous loops that one must go through to filter information and keep some of it private from, say, a boss/co-worker/professor/parent and yet still share it with actual "friends".
Google took all that problem of going into the privacy settings, setting up groups of friends, etc, and made it a visually satisfying drag and drop system. This has little impact on me since I don't use facebook to share photos and post what I'm eating for dinner or if I'm out and about, and instead am the annoying political facebooker that I'm sure most people filter out, but to whom most of my posts are readily visible. I don't care very much if people know I'm an atheist or know I'm libertarian, and so on, and these are the things I post on there. What concerns me is my actual private life, which I don't post on there.
It's possible this would be a distinction with google plus for me that would be worth using, but I imagine this difference is far more important and noteworthy for the average facebook-er. At least until (if?) Zuckerberg figures out that this is the principle market share problem he has going forward. Complex privacy settings and poor filtering controls that can be simplified into an intuitive interface? Check. Google's got that.
Otherwise, it's pretty much the same sort of stuff. "+1" instead of "likes" is a little more satisfying. More of a novelty satisfaction than a meaningful one. Other than the difficult decision of "liking" some story or post about something saddening or tragic, in the same way that Netflix users indicate that they "like" Schlinder's List but end up watching "Fast and the Furious" or some similar piece of crapulence. Or people listening to the car stereo self-report listening to more talk/news or jazz than the popcorn syrup stuff that they actually do listen to most of the time. This semantic change allows us to preserve our outward signaling that we are not all self-absorbed egomaniacs while the interface change allows us to continue being self-absorbed egomaniacs.
Bottom line: I suspect it will end up being more popular as it's more in line with human nature than total openness and transparency.