[Jschwa]

@tylerstalder left this in the comments of the post:

http://www.slideshare.net/padday/the-real-life-social-networ...

It's an excellent deck from a Google UX Engineer that describes the scenario you are talking about with sharing with "everyone except for parents".

The problem that the deck illustrates is that the breakdown isn't just Parents and Everyone else. Each person has 4-6 different groups, each with its own level of appropriate or relevant content. The trick is designing to account for each.

[stcredzero]

I think the trick is to leave a path open for a person to discover that their personal social Venn diagrams are this complex. There should be several stages. At each stage, a user discovers some pain (I wish I could leave my parents out of this) and then discovers an easy solution. (Ah ha! I can use this "parent" tag and then it prompts me so I can choose to not let my parents see this.) The user is pleased, until they discover their next pain. (I don't always want all of my friends to know about...) The end result is that you've solved the user's pain several times over, and so they love your product.