So Microsoft and Yahoo announced they'd agreed to make their messaging tools communicate--or merge.
AOL, which is investing a HUGE amount of its strategy in AIM, was conspicuously missing from the announcement.

Susan sez: Is this about competition--or acquisition/investment?
Me vote for acquisition/investment--my guess is that the strategic co-venture Microsoft is exploring with AOL will deliver AOL's audience eyeballs up to MSN tools over a staged 2 year phase in and will allow AOL to pretend it is a successful content company as it transfers its music and entertainment teams (the ones who get it) into a merged group that can deliver content to both entities.

Update: Scott Rafer has a similar post here.

update 2 -- Richard Lusk says "It looks like it may be a AOL+Google+Comcast mashup."