Personal information exchange - the essential missing part of social networking profiles.
When people communicate face to face, it is natural for them to reciprocate and exchange information bit by bit. For example, if the other person asks me where I'm from, I ask the same in return; if I ask the person's occupation, I expect to be asked bout mine, and so we continue disclosing detail after detail to each other.
This trading of information (in barter) happens naturally when we communicate face to face, but we have no time-efficient way of doing this on-line. All what modern social networks provide is the possibility to set visibility of your static information of your profile, and if you want to share something else, you have to retype or copy-paste the information you want to share each time you want to do it, and that's a waste of time.
So, here is an idea: profiles should contain a "magic FAQ." Any visitor of your profile should be able to add a publicly invisible question to your magic FAQ; you would be notified, and have an option to answer it, both replying the questions and building your FAQ at the same time (one shot-two birds). The publicly invisible conversation could continue much like a hierarchical comments, forming a hierarchy that you possess. The next time someone asks a similar question (i.e., adds a question to your FAQ), you could tell the system that it's just another way to ask the same thing, and reuse your previous answer with a click of a button. A different follow-up question? No problem -- the data structure like pHTN (probabilistic hierarchical task network, which is just hierarchically arranged lists with probabilities of each element in the lower level of the hierarchy) can handle this, and even learn to auto-suggest you to reuse your most preferred answer (three birds?).
An expected result of this idea, is that even celebrities, who don't have enough time to chat with every fan, would suddenly have time to communicate personally, in this semi-automated manner.
P.S.: This idea is a result of mass spamming, and at the same time thinking of how to save people's time.
[Reminded by Profemaile, 2005]