From Blue-IT.org Wiki
This is for Ubuntu 10.04 and up.
Use the webupd8 ppa.
Then you can easily install the folloing gimp addons
sudo apt-get install gimp-plugin-registry gmic
What Gimp cannot do
Gimp lacks some simple functions like adding pillars, arrows, shapes and other little graphics that you might need.
Copy and paste existing graphics
You can install e.g. openoffice cliparts and then import these shapes into gimp. On ubuntu you'll find these graphics under /usr/share/openclipart. Add a bookmark to nautilus folder and select icon view, so you are able to easily browse to the cliparts.
Make your own graphics. There are a lot of tutorials in the web, how to do this.
Install destop publishing software
Therefor you have to use programs like xara, scribus, dia or openoffice draw. They can easily installed e.g. with ubuntu out of the box( or use automatix2).
Each of this program is designed for publishing, so they will produce letter size output, e.g. for letters or catalogs. Each of them uses its own file storage format.
That's why you have to use the import features to use your gimp edited e.g. png graphic and the export feature to get a png picture again.
Round Edges with background shadow
ScriptFu -> Decoration
- Script Fu -> Shadow -> Shadowed
Selection -> Rounded rectangle
- Selection ->Invert selection
- Selection -> Cut