Arguably Gimp is the best image editor in Ubuntu ( You can do a lot more than this )
Currently Ubuntu12.04 is running stable version Gimp 2.6.1. Great news is that Gimp 2.8 is available but not directly available through Ubuntu repository. So I tried 2.8 version and its much better and lot of performance improvements. single-window mode is the best features of 2.8 version.
Install Gimp 2.8 from terminal
Open a terminal and run below commands
sudo apt-add-repository ppa:otto-kesselgulasch/gimp
sudo apt-get update
sudo apt-get install gimp
Now you have successfully installed Gimp 2.8 !
Open dashboard and type Gimp. See below screen shot of Gimp 2.8 in single-window mode.
Gimp website — http://www.gimp.org
For Gimp 2.8 features — http://www.gimp.org/release-notes/gimp-2.8.html
Hope Gimp 2.8 will include in the Ubuntu Repository soon. Please share your experience.