Right now you can only connect to the AIM/ICQ network using this gateway, there is no XMPP Federation. This means that you cannot talk to users on any other IM network at this time, including Google Talk. Hopefully AOL will add support for XMPP Federation in the near future.
Still, this is a welcome development. While at AOL, I worked on the initial design for this project, and it's good to see it live. Note that the gateway is still not officially launched, so it may be unavailable from time to time.