- the notification area icon (it's not the system tray)
- the menu item in Windows
In addition the sounds will change.
Having run the new Skype UI for a while now I much prefer it to the Lync 2013 UI, my call out features are the Call Hover window when you are in a call and pass focus to another application, this stops your scrambling about trying to find the active call to mute/unmute, hangup!
and the new emoticons :-D