If I had to summarize:
- social graph is a modelling problem and it is very hard given the kind of interactions people do.
- having a generic social graph is equivalent to coercing people's behavior into a model... which will lead to complications in usability.
- a generic social graph has huge potential for advertisement and marketing, but that doesn't really benefit the users much (facebook / google+ fall in this category).
I saw something similar in a talk by 4chan's creator that social interactions define the social graph... not the other way round.
Any thoughts, comments?