This is more a general question that I would like your opinion on.
I'm extremely impressed with facebook.com, and I wonder if Wordpress will ever develop into something similar. The only real open source alternativ to facebook.com is elgg.org, but it doesn't seem like a completely mature product yet.
Right now the only real cross blog-interaction in WPMU is users commenting on each others blog, and various cross-referencing feeds and links.
The WPMU "Friends" plugIn is an example of a "social software" plugIn that binds users more closely together and in turn feeds more activity. However, I would also love to see plugIns like:
* Ability to create networks around certain topics (I guess you could just create a blog for, say, New York, but it doesn't seem to be the right way).
* All sorts of activity plugIns. This is what is really impressive with facebook. Everytime you log in you get a complete view of all the activities of your friends.
* Marketplace. One could argue that this has nothing to do with Wordpress, but the ability to buy/sell stuff really enhances the interaction.
Do you think WPMU will eventually move in this direction (or maybe it already has and I haven't noticed