A few interface and tool changes were introduced in GIMP 2.6. They are not only cosmetic, but intended to improve usability.
A new "Empty image window" is created to host the menubar when no image is open. It allows you to drag and drop files to open them.
Toolbox and Dock bars now are tool windows better prepared to stay on top of the main windows, not appearing in the taskbar, improving the on-screen organization. This is the default GIMP interface just after starting it.
Now you can pan the image beyond its border when a utility window covers a portion of the image or when you paint on the border of an image that fills the entire window:
There are a few minor interface changes that are worth mentioning here because they improve usability:
The Dialog menu is now named Windows.
History of recent closed Docks, and the ability to reopen them.
The zoom ratio can be manually entered in the status bar.
If you use the context help function from the Help menu, you can click on an item in the GIMP about which you want more information, and it will connect you to the GIMP website via the GIMP browser or a standard web browser.
Tabs can be locked on Docks to prevent accidental moving.