I personally use them a lot. For example, I share immediate family-related photos and posts with the Family circle, general family stuff with the Extended Family, some stuff with Friends, some with Colleagues. It's useful and powerful feature, but requires skills similar to the email Inbox organization which some people seem to find too hard.
It's not that it's too hard, it's just not something I want to worry about. I think some people like to really organize things and some see it as a hassle.
For myself my inbox has essentially two folders. Inbox and Archived. My facebook lists is just friends and my google plus circles is just whatever the default is.
I don't want to think about who I'm sharing things with. I either share it with everyone on a social network or send it as an email to specific people.
