Good post. The point you make about sharing contacts across networks kind of depends on how many social networks you’re in and what you use them for.

I understand the various setting options of Facebook and the nature of LinkedIn, but I don’t think that any single network has a single purpose.

Don’t discount smaller, more intimate services such as MobileMe as a way of sharing the more personal information about yourself – therefore giving you the advantage of using the bigger networks in a variety of different ways, i.e. to tell the story of you, they way you want to tell it.