I thought of an interesting idea for Minecraft.
A mailing/trading system based on training birds...
It'd have a GUI that lists all of the players on the server, and allow you to gift and exchange items from long distances.
First you would hatch a bird, then wait for it to learn to fly. And then you would make packages to deliver the items in.
The more you raise your bird, the quicker it is. The more birds you have, the more you can send.
Another idea is to have them deliver to mailboxes.
It would be useful because it would allow traveling adventurers to support towns while they are away. It'd make a better player connection in the servers.