> Google+ account not required

I think this is misleading on Google's part...

From outward appearances, everyone that has a Google account (aka. GMail) has a G+ account, and the only thing that changes when you "sign up" (or otherwise activate) is that you can log in to it yourself.

I was on G+ for awhile, but I've now since disabled it in my control panel, and yet people still share crap with me (as I'm still in their "circles") -- it just goes to my email. I think the service is always-on, they just don't let you into the UI if it's not "active".