Not only do people continue to use AIM -- entire companies use AIM.
The last two game studios I worked at mandated this. Everyone in the company either already used AIM, or created a new account with the company initials as a prefix.
Skype chat is superior, I agree. But AIM solves "the communication problem" just fine, too.
I would seriously question the integrity of any serious company's IT department if they just had everyone use AIM (the proprietary branded IM service -- not IM in general).
Or it was, not sure if the new-new Webex one is.
The only things I've used in GMail/Google Apps chat and IRC. I love IRC. I can private message people, we have rooms for different projects as well as idle chat area for random chit chat.
I guess I just see AIM as really juvenile but that may have more to do with the gaudy AIM Windows clients.