You can take a chest with you to the nether, drop it, put your nether ores and glowstone safely within as soon as you mine them and empty your inventory without having to return all the way to the portal. (Note: an Alchemy Bag may be preferable.)
It can be used to share items between multiple bases. You can store all the mine carts for your railway stations in the one chest and have them accessible from any station. You could have a public food chest, and everyone on the server could access it at the same time.
Each pad can be recoloured by using a dye on the pad or by using the following recipe with the three dyes in the crafting table.
If one chest is opened all chests with the same code will be opened.
As they are made of obsidian, Ender Chests are mined using a pickaxe (preferably diamond). You cannot change the code or break a chest that is currently open.
In Minecraft 1.3, a similar Item was released To Vanilla (Default) Minecraft but with some different features. It does not have the Colored Wool at the top and are player specific. So if you open one it will be empty (Until you put something in it) no matter how much other people put in it. A more detailed definition is in the Minecraft Wiki.