Facebook changes stuff all the time, and thus I would have to keep tweeking the settings. Instead, it all just goes into a circular file at Google which I empty from time to time.
And that's why Google+ circles don't aren't really a game changer - it doesn't significantly reduce the friction of managing notifications except for the small segment of people who are already interested in managing those notifications.
I had all e-mail notifications turned off from when I first logged into facebook. When they added the new groups I started getting e-mails again. I have to go into settings about once a month to turn off the e-mails in some different part of facebook.
And that's why Google+ circles don't aren't really a game changer - it doesn't significantly reduce the friction of managing notifications except for the small segment of people who are already interested in managing those notifications.