In his post Microsoft Goes Social discusses some of the design decisions we made when adding Social Networking to MSN Spaces. He questions the decision to not use people's instant messaging contact list as their public social network. Specifically he asks

2.  Dare warns about automatically converting a Buddy List into a social network.  Hmmm - we’re about to find out how that works with AIM.  This notion of the Buddy list as social network tantalizes me - the results will be fascinating.  Dare claims it will be a 'privacy nightmare'. I don’t necessarily agree with him - but (as I said above) we're about to find out if this is true - in spades.

I can describe why this unsettles users by painting out a scenario. Now imagine that I get contacted by a recruiter for one of our competitors by email and she asks for my IM contact info so she can give me the sales pitch on why I should switch jobs and perhaps figure out an interview schedule. When I get the request to add her to my contact list, what I have agreed to is for her to be able to talk to me online and see my online presence. If later on the provider of the instant messaging service adds a feature that exposes people's relationships to the public then my relationship with this recruiter would be outted even though I never agreed to be listed as their "public friend".

Of course, nothing stops the recruiter from just blogging about our relationship or creating a blogroll of "people I'm trying to poach from Microsoft" but that's just her word against mine. With publicly exposing her social network, it is now confirmed that we have some sort of relationship. That's not what I agreed to when I accepted her as an IM contact.

A lot of this is gut feel from a lot of us who use and build these products. However I'd rather err on the conservative side than piss off our users in a crass attempt to increase the usage of one of our features.