As Officially Announcement says:
This latest version incorporates many bug fixes and we’ve improved the general stability of the product.
Here’s a sneak peek of what you can expect in Messenger 11:
Invite your friend to play a game – In addition to instant messages, text messages, voice and video calls, you can now play popular social games such as Mafia Wars and Fishville right within Yahoo! Messenger.
Keep up with friends wherever they are – View, comment on and like updates from Yahoo! Pulse, Flickr, Facebook, Twitter, and more, all from right within Yahoo! Messenger.
Post one status to multiple social networks – Share your Messenger status simultaneously on Yahoo! Pulse, Facebook, and Twitter.
Chat with Facebook friends – In addition to your friends on Windows Live, you can now IM your Facebook friends. Continue your conversations on the go using Mobile Web Messenger, SMS Messenger or Yahoo! Messenger App for Android.
Always be available – Stay signed in to multiple PCs simultaneously so you never have to miss a message.
Easy access to recent conversations – Retrieve all your IM conversations from any PC where you have signed in to Yahoo! Messenger.
Personalize your experience with fresh new skins – Express yourself and show off your personality with one of the 7 newly added messenger skins.