1. All new things have a shelf life.
When will the novelty factor erode? Historically these issues go way way back. The Freemasons secret handshake was an early solution to the trust issue. When we look at the social networks that have existed in the real world throughout history and asked “what is different this time?” the answer is “medium”. The evolution of consumer behavior on the Internet has tended to go from “I can do it differently” to “so what, I know it, and how different it is?”
2. When will the visibility and trust be unsustainable?
This is the most critical question determining the business value of social networks. However if trust erodes, what is the point of a network? The social network is valuable because it is exclusionary. MySpace is cooler/more valuable because older folks are not there, and that implies some optimal network size. However if this is true, it is a reverse network effect and that will have a crushing effect on social network valuations.
3. Entry requirements for multiple networks?
Most of us need to be members of multiple networks and these changes as we get older (school to college to work to parenthood, etc.). Something like OpenID is part of the answer, but also tools to transfer our digital stuff between networks and decide what stuff goes in what network.
4. How are we at ‘an arms length’ from certain people:
A network that is only strong ties (everybody knows everybody very well) is not valuable on its own. In companies it leads to stagnation, in social circles it can lead to snobbery/prejudice. The outsider with a new perspective is valuable. This is why blogging comments are so effective and some of the innovation around rating comments is interesting; it is porous rather than exclusionary, but the new tools may filter out the noise.