Version 5.3 of Skype for Windows has just been released, with the main emphasis of the new release being improved call quality, and the quality of video received by mobile Skype users. Presumably one party of the video call must be using Skype for Windows 5.3, though.
Beyond improved call quality, not much has changed. You can now see your friends’ presence icons when contact cards are collapsed, and the topic editing button is now always visible on the conversation header. For a complete list of changes, hit up the Skype Garage blog.