If you are an Apple Ecosystem person (iOS + OSX) you'll love it. Messages is the replacement for iChat and it allows you to have the same conversation with anyone that is in the iOS ecosystem across all your devices all at the same time.
So here's how to get the most out of it.
Open Messages, the icon looks like the above picture. In your preferences, you need to set up your iMessages account. I use my iCloud account, (me.com), but you can use any email address I believe. So, add your iMessages account. Enter all your email addresses there on the bottom, it may ask you to verify them (at which point Apple will send you an email through the account that you entered to ensure you actually own that account):
The next setting to pay attention to is the "Caller ID". Pay particular attention here because you are going to want to set that to be the same as your iOS device. This is the awesome part where everything becomes one.
Then you should be good to go on the desktop.
Now let's setup iOS to be exactly the same. So go into your Settings in iOS, and go to Messages. It should look something like this:
Tap on that with your finger. Take a look at the settings and set those up how you want them.
But you'll see a section that says something to the effect of "Send & Receive":
Note: I am using the developers preview of iOS 6 to take these screenshots, so your screen will look different.
Go in there and add all the same email addresses that you added on your Desktop. Also, on the bottom, you will see "Caller ID". Set the Caller ID to be the same as what you put on your Desktop. On your iOS devices, I'd suggest NOT setting it as your phone number. I set mine as my iCloud email address, as that address has my phone name right in it and it's pretty obvious to the recipient who is sending a message.
Repeat this process if you have multiple OSX Desktop machines (laptops), iPads, iPhones, whatever.
After this process is complete, whenever you have a conversation through iMessage, it'll be the same on all your devices. Desktop, iPad, iPhone whatever. When people answer you back, it'll go to all your devices.
This allows you to start a conversation on your Desktop, pick up your iPad, go to a meeting, have the same conversation going on seamlessly, no syncing with anything, and keep going in the same conversation. Have to leave the meeting to go somewhere? Pick up your iPhone, because the conversation will be exactly the same.
If everyone in the ecosystem did this, it would be a seamless network of interaction between everyone. I love it. I hope that Apple will streamline this setup process a little bit, (like unifying the phone number and email address, and allowing the setup of the accounts in one place, and those settings pushed through iCloud to all devices, so that everything is the same)
One more thing.
Open up Facetime. Open up your preferences in Facetime, and set everything up the same way. That way, your Facetime is also ubiquitous everywhere.
Please leave comments below.