I haven't used AIM in ages due to the amount of spam bots that frequent the network. However, it's nice to know that my account is still there and that Messages was able to pull in my entire buddy list. It also would have been nice if Messages had been able to pull over all of my existing iMessage history from my iDevices. As it stands, the app window looks a little bare when you initially start things up.
To send a message, enter a recipient's name. As you type, Messages will filter your contacts and you can select the one you want. Messages can be sent to multiple recipients.
After a message is sent, the conversation shows up in the left pane and the individual messages show up in the right pane. You can type a new message at the bottom of the right pane.
You can get contact details by right clicking on a conversation participant (other than yourself) and choosing Get Info.
Messages lets you set custom alerts for each person you exchange messages with. But note: this feature works only with Messages and iMessages. It's not for AIM or any other IM service.
Messages lets you choose a different default method of contact for each of your contacts. Each number or address is a different profile, and what Messages can do is listed with each.
FaceTime, Apple's video software for the iPhone and iPod Touch, is integrated into Messages. You will need to configure the camera, microphone, and headset (if you're using one) before you start a FaceTime conversation. If needed, you can set a bandwidth limit so you don't clog your outgoing network pipe.
Messages lets you configure its behavior based on specific system events. You can even run a specific AppleScript script when a specific event occurs.
Messages lets you control how conversations appear. The app also will keep a transcript of each conversation, by date, in the iChats folder.
You can configure and use Messages with different messaging accounts. It has built-in support for AIM, Yahoo! Instant Messenger, Jabber, Google Talk and also has support for Bonjour.
Adding a messaging account to Messages is as easy as selecting the account type and typing in your credentials.
A wide range of general preferences lets you set up Messages the way you like, even including what to do when fast user switching is used, and whether to let others know you've returned to your computer.