Wait... isn't that kinda old??. Yes, it is.. but in the past you had to log-in to your AOL account to open a "portal". But with this new service that is no longer necessary!. Furthermore, you can add AIM users to your chat list as easy as adding Gmail users (for instance, add "username"@aol.com in your Chat box and you're good to go).
According to Google, not just in Gmail, but you can use this feature in few of their other services such as iGoogle, Orkut, and Google Talk (on Android Phones). Because of the API "collaboration", AIM users can add Gmail users the same way in their accounts as well.
But if you had a massive list of "friends" then adding the one by one is a painful task. In that case, this official AIM Buddies importer is a must. Good luck :).