We are all familiar with Messages for iPhone and iPad and now Apple has brought Messages to the Mac. Messages for Mac is technically in beta, but it's a public beta which means if you're running OS X 10.7 Lion or the developer preview of OS X 10.8 Mountain Lion, you can download it now and give it a try.
If you use Messages on the iPhone or iPad, then you already know how to use Messages on the Mac. In fact, messages for the Mac is nearly identical to the iPad version.
Messages on all your devices is a fantastic idea, however it still needs some work. Namely, when someone sends you a message, a notification is sent to all of your devices. This would be fine for the first message, but even if you are actively using Messages on your Mac, your iPhone and iPad will continue to beep and chirp with every new message that comes in. This gets extremely annoying very fast. Apple needs to figure out a way to recognize which device you are actively using and disable notifications to all other devices. I'll be honest, I won't be using messages on the Mac very often with its current design. The experience is and maddening.
That's not to say it isn't a good start, though. Messages for Mac is technically in beta, so hopefully Apple will make some changes before the final release.