Too little, too late...
AOL, Yahoo And MSN To Integrate Messaging say the headlines; the small print gives a different tale. To actually get this integration one has to buy and run some server software from Microsoft that then passes IM traffic to AIM, Yahoo, and MSN.
This form of setup can be useful in an enterprise scenario. But, it can already be done using an in-house Jabber server with gateways to the other services, so this is hardly news. The press release mentions how vital logging of IM traffic is in the financial business, but omits the essentials like SEC compliance!
Jabber has been able to provide SEC compliant archiving since January 2002, so AIM, MSN, and Yahoo are still playing catch up.