In his substantial status report on social networks applications, he shares his mindmap on SNA's (at Fast Company.com)

Dave says, people are looking in Social Networks mainly for
- Finding people to love and live with
- Finding people to make a living with
- Finding people who share important or urgent affinities ...
- Enabling powerful virtual collaboration
and he is missing most
1. Inflexible, tedious information architecture ("Why is entering this field mandatory?")
2. Profile poverty ("This tells me absolutely nothing of value about this person")
3. No separation between What I Have and What I Need personas (the information about you I care about depends on whether I am 'buying' or 'selling' -- even classified ads 'get' this)
4. Lack of harvesting capability ("Why do I have to enter this again?")
5. to 10 ....
read more (all the rest of his status report) on his blog post