Martin Gräßlin, the main KWin developer, has written about the changes in the past week for the compositing window manager.
The main new feature is "kwin option to save vertical space: merge window buttons into menu-bar." The basic premise is the moving of menu buttons (e.g. File, Edit, View, History, Tools, Help, etc) into the same bar as the window's title bar with the close/maximize buttons. It's part of this bug request.
Some other window managers and applications have supported this with menu buttons in the window decorations while now it's coming to KDE. Martin says this will work with KDE 4.10 to be released next month.
For KDE 4.11, virtual desktops have also been re-factored. "For example a refactoring of virtual desktops landed in master. The management of virtual desktops has been split out of the Workspace class into an own module."
Plus a variety of bug-fixes and other work has been going on for KWin over the past week.