This new version includes:
Tabbed IM windows: When you have two or more conversations going on, they appear as separate tabs in a single window. Less clutter for your desktop! Plus, you can drag a tab out and make it into its own window (or drag it back in to consolidate). Tabbed conversations are a preference, so if you prefer having one window per IM conversation, you still can.
Chat rooms: Yup, the same Yahoo! chat rooms that Windows users have been using are now open to Mac users.
Message archiving: All of your IM and chat room conversations can now be archived on your computer.
Improved stability for webcam and file transfer: There were issues with these in the past version so the team did a lot of bug fixes and under-the-hood work to improve them.
More emoticons: We added in the additional emoticons that are in our other versions of Messenger, so Mac users now have them all!