GIMP 2.5.0 is the first release from the 2.5 development series. It gives developers and interested users a view into the current development towards GIMP 2.6.
What's New in GIMP 2.5
The most notable change in GIMP 2.5 happened under the hood. The color tools in GIMP have been ported to GEGL. This does not yet have much impact on the user experience but it is a first and important step forward. With full GEGL integration GIMP will finally get support for higher color depths, more colorspaces and eventually non-destructive editing.
With the help of the UI team, the Toolbox menu has been merged into the image window. GIMP now always keeps an image window open and the default configuration treats the toolbox and docks as utility windows.
An often requested tool for simple polygonal selections has been added and work has started to improve the text tool.
More info @ http://www.gimp.org/