The open source image manipulation application, Gimp, has always had a rather gimpy user interface. But the next stable version, 2.8, is going to see a significant overhaul in the user interface department.
Gimp 2.7 is a developer version of the application, it gives the open source community an opportunity for a sneak peak at what's ahead when 2.8 comes out.
From the release notes:
There have been some significant changes to the UI. The docking bars have been removed and replaced with overlayed highlights. The dockble drag handle has been removed and the dockable menu button has been moved up to the tabs. A new Automatic tab style has been added which makes dockable tabs use the available space. It has been made possible to have many columns of docks in a single dock window. To make dock window titles managable, only show the active dockable in the dock window title. A single-window mode has been added (still in the works, in particular, it is not possible to start up in single-window mode yet).
Support for layer groups have been added. They allow you to organize your image into small parts. Still some things missing, like allowing to apply layer masks to groups, and a PDB API.
Text editing with the Text Tool is now performed on-canvas instead of in a separate window. The editing on-canvas is rather sophisticated and tries to mimic text editing capabilities of GtkTextView. There are still some polishing left to do here, but it works rather nice already. This feature was developed during Google Summer of Code 2008.
There's a lot more happening with the UI, you can read the complete release notes here.