The main improvements Skype is delivering include much improved audio call quality, better video support, and improved chat synchronization. For video specifically, Skype has spent time implementing support for a much wider range of webcams, so if your camera didn’t work before today you might be surprised to find it does in Skype 4.0.
Visually, Skype has received a new Conversations View, which brings all chats into a single, unified window (you can revert to the old view if you prefer). There’s also a new Call View, presence and emoticons have been redesigned, and you can now store and view numbers within each Skype profile."
Link to Original Source