I just found a slightly dated paper on AOL interoperability and standard adoption, particularly with respect to Jabber. Wishful thinking? I'm betting AOL will wait for two things: (1) for an IM standard to have an RFC number, and (2) to no longer be clearly #1 in the market, as it is now.

A year ago, AOL was clearly the market leader, but MSN and Yahoo were reportedly growing faster (together MSN and Yahoo have more users than AOL). Now, Yahoo claims the most "workday IM users" (also see here, and Jupiter Media Metrics shows that MSN is still gaining.