Google+ is continually making major changes to its interface and for some reason, people actually like them, as opposed to whenever Facebook makes any kind of non-minor change, which results in people swearing it off. Just last week, Google+ implemented a complete redesign with a bunch of new features, although I personally think that the old one was much more organized. That said, if Facebook dies out for whatever reason, Google+ has the best chance of displacing it, assuming it doesn't die first, which I think is unlikely.