The Null Device
Today, we increasingly live in a world of software-mediated social interaction, and at this moment, Facebook is one of the largest such systems. As more people join Facebook, and it becomes an increasingly indispensible utility for connecting people, and the range of people one is connected to becomes much broader. Whereas once one's Facebook friends tended to be college buddies and close friends, they now include coworkers, family members, old schoolmates, neighbours and others.
Facebook's privacy options, however, haven't kept up with this change. When you post to your Facebook profile, there is no way to make posts visible by only a subset of your Facebook friends. So you're faced with the choice of self-censoring your posts to a level suitable for all users. You might not want your parents or employers to see photos of you partying, or might not want to bore your non-technical friends with talk about specialised subjects a subset of your friends would be interested in. So the end result is that Facebook is reduced to the lowest common denominator of subjects suitable for all audiences; things that won't shock or bore anyone. This leaves no suitable space for a large set of discussions: in-jokes between closely-knit groups of friends; specialist banter about C++ or football or archaeology; or even personal discussions you wouldn't necessarily want to share with your coworkers or casual acquaintances.
There are better ways to do this. The photo sharing site Flickr allows users to tag certain friends as "Family" or "Friends", and make some photos only visible to those groups. The LiveJournal system goes further, allowing users to define arbitrary numbers of friend groups and control who can see each post individually.
Facebook needs something like this if it's going to scale. It need not be an intrusive feature; a checkbox to the right of the "What's on your mind?" box, opening a "Show this post to: Everyone / All my friends / (groups)" drop-down, would suffice quite elegantly. (Something similar, of course, should be added for photos, notes and such, and made available to application developers.) This would make Facebook much more broadly useful as a tool for connecting people across the wide spectrum of social relationships they have in their lives.
Anyway, to wit, I have done the obvious thing about this deficiency and created a Facebook group about it. Perhaps if enough people join, the Facebook developers will listen.