The Future of Google+? Log in, look around and log out 15 years ago
IMHO, that navbar might just be the thing that would somehow make Plus popular. I've got my Gmail tab open at all times, but I don't want to have the Plus tab just to see if someone mentions me. That's why I'd forgot about any new social network.
But on the other hand, do I need notifications in my e-mail? No. And if notifications get too much right in my face, I'll probably disable Plus somehow.