If you like the minimap which shows you an an overview of your files that comes with Sublime Text 2, you'll be glad to know that such a plugin was released for Gedit.
The plugin is called Text Map and displays a navigable thumbnail of the entire file in the side pane but for now it doesn't display the syntax highlighting as well (like in Sublime Text 2). However, the plugin is currently in beta so it will probably be improved in the future.
To install the plugin, download it, extract the archive and copy the extracted files (files, not folder!) to the ~/.gnome2/gedit/plugins folder. Then restart Gedit and activate the plugin from the Gedit Preferences (Edit > Preferences, on the Plugins tab enable the Text Map plugin).
Once activated, you can view a thumbnail of your file by activating the Side Pane (F9 or go to View > Side Pane), then switch to the TextMap tab.