The biggest feature I've been working on for MSN Windows Live shipped last week. In his post Friends beta (Australia) Mike Torres writes

I'll be talking about this feature at length in coming months as it rolls out more broadly, but for now check out what Phil has to say about it (with screenshots):

Social Networking Trial
One of the reasons to be here this week has been that we were getting ready to deploy our first social networking trial, specifically within the Australian market.   This new functionality is an extension to the existing Spaces service and is exposed as a module that one can add within one’s Space.  Our approach to social networking is designed to enable a way for customers to communicate and connect in more meaningful way with their circle of friends and in particular their friends and their friends’ friends.    We are doing this by adding this feature to our existing network – be it Messenger, Spaces or Mail rather than build a unique social network.

If you've received an invite to join and already have a space in China, the U.S., or any of our other markets that aren't named Australia, you won't be able to accept the invitation just yet.  We realize (quite frankly) that this sucks... but it won't be this way forever.  If you're in Australia, you're probably having some fun right now!

This is also one of the features that has changed a bit since our book went to print.  On p136 there's a section on "mutual friends" which isn't applicable anymore.

Mike and I worked on the design for this feature while Matt and John were the kick ass developers who did the heavy lifting by actually writing the code. If you want to see what this feature looks like on an actual space check out http://spaces.msn.com/darestestspace/friends/ and http://spaces.msn.com/bruce-a-h/friends/. As with everything in Windows Live you can expect that this feature will be integrated into more than just MSN Spaces.

It's been an interesting ride getting this feature out of the door and there are some design decisions that stick out when I look back at the last few months. One design question was how to deal with allowing people to have multiple social networks. People told us they have friends, coworkers, drinking buddies, acquaintances, etc and would like these reflected in their 'Friends lists'. In addition they told us that these groups overlap so you may consider Bob a friend and a coworker but Lucy is just a coworker. We eventually decided to go with tags by allowing users to simply label people with whatever phrases or keywords they felt applied to their Friends. We thought this was a lot more elegant than having people deal with multiple social networks or subgroups within their social network.

Another interesting discussion that showed up once we started testing the feature with coworkers and in focus groups was that people didn't like being called someone's friend without having given them permission. The original design for the feature followed the LiveJournal model where you had friends [people who you added to your social network who hadn't reciprocated] and mutual friends [people who you've added to your social network who have also said you are part of theirs]. Mike and I thought this model was similar to how blogrolls work today. There are people in my blogroll who didn't have me in theirs and there are others that do. Lots of people freaked out about this, specifically they didn't want their picture showing up in someone else's space if they hadn't given permission. We played around with different models for differentiating 'friends' from 'mutual friends' but eventually gave up and now just have one model. When you add someone as a 'Friend' they don't show up on your list until they accept and add you to theirs as well. Mike and I disliked paring down the feature in this way but almost everyone else preferred it to the 'mutual friends' model.

One question we got a lot from people at MSN was why the Social Network wasn't simply people's Messenger buddy list. The explanation for this is quite simple, it's because it is a privacy nightmare. When I agree to be your messenger buddy, the social contract is that we can see each others presence and IM with each other privately. To suddenly switch on a feature that changed the nature of that relationship into a public one is extremely disrespectful to our users and would piss them off. Heck, it would have pissed me off. Mike has a great analogy for why this is a bad idea which I'll let him tell when he starts blogging about the feature.

Of course, the decision that took the longest was what to name it. Eventually the powers that be settled on 'Friends' but I personally would have preferred some of the other names we threw around like 'Social Circle' or 'Peeps', the main problem was that none of those terms translated well into other languages and we are a multicultural service.