WPF Docking library first stable version is about to get posted. It enhances new valuable features like floating windows. With this version a dockable pane can be hosted in a separate window and than it can be docked back to main window. Also contents in pane are now arranged in a restyled tabcontrol which shows an icon in tabitems.
Here you can see a pair of screen shots which show docking in actions:
Library version 0.1 will be posted to CodeProject this weekend.