Is there a list of SO-people currently online?
I think if there were a list of SO people online then it would be a short step away from asking to contact them, friend them, follow them, whatever them ... and we all know where that goes, it becomes social networking.
There are details on getting in touch with SO users interested in social networking on SO - is that any help?
I would find it quite interesting, just a little discreet thing saying "23k users online" somewhere.. I think it's a nice idea
Nowadays you can use the chat for a similar functionality. Look for it at the bottom of the specific site.