Does anyone still actually use AIM to sign in to their AIM account? I've found the AIM Express client useful occasionally when I happen to be on a strange computer (though nowadays I mostly use the AIM iPhone client when I'm AWOL), but on the desktop it's been Adium for longer than I can remember.
Still, if you'd rather do the official way, AIM for Mac 1.1 is out now. There are a few bugfixes -- ICQ accounts had an issue signing in, apparently, and there were a few font and display issues fixed. And there aren't too many new features, though you can now leave notes in "Edit Buddy" fields and the Buddy List search got improved. Unfortunately, it looks like, according to the screenshot they posted, the Buddy List will also blur out all the names on your Buddy List, which seems really inconvenient.
The app itself is still in beta, though you can't really go wrong with instant messaging -- either your messages get through or they don't, right? You can download it now, or if you're already using the 1.0 client, you'll get notified automatically.
Disclaimer: TUAW is owned by Weblogs, Inc, a division of AOL. We were kidding about that blur thing, AOL -- we know it's just for the screenshot.