The solution is so retardedly simple that I'm shocked no one has patented it: Take a page from real life and give users the ability to create multiple "views" of their profile. For each "friend," specify which views they are allowed to see, and for each new bit of content you add, specify where it belongs.

So, let's say I create 3 views:
1 - work/academic
2 - family
3 - drunken debauchery

The general public and creepy guy from work can only see 1, mom and dad can see 1 and 2, and my closest friends can see 1, 2, and 3. Content generated by your friends (pokes, walls, photos, etc) are restricted to whatever view that friend is coming from, so your wild friends don't accidentally bust up your Chaucer reading group.

Just like real life, none of your so-called-friends know which view they're getting, so there's no awkwardness. They just think you're boring or don't post much.