I've been working on a tool named autoglade that could be of help to
simplify application development using glade as the interface designer.
You can download autoglade from http://sourceforge.net/projects/autoglade.
A basic tutorial can be found in the wiki: autoglade tutorial - first steps.
As the tutorial demonstrates, nautilus actions can be greatly enhanced using autoglade generated GUIs. You are not limited to zenity anymore.
More to come.
Comments, suggestions, critics, bugs, fixes, etc are gladly welcome.
Please use autoglade's mailing lists.