AIM is working hard to collar the all-important youth market, and has respun the AOL tools into a Nerdvana style client (see various Nerdvana postings) where everything is based on the buddy list. Although (for shame!) it is not available for Mac OS.

I expect this to be one of the areas of future battle between MSN, Yahoo, Google, and AOL: who will develop the best integration of communication, collaboration, and coordination tools based on the "buddy list is the center of the universe" motif?

They are focussing on communication first (leaving aside blog-style, asynchronous style stuff, which doesn't look like it is integrated yet). What is missing to date: calendaring, media sharing (real-time or slow-time a la Flickr and Last.fm), and project collaboration (a la Basecamp). Inevitably, these will all coallesce. No one has the who story, and whoever releases the critical mass beta will likely destabilize the marketplace.