Using something like Bonjour, and a small bit of software on both the target and source computer, drag and drop a file onto an icon (like Cloud.app) and have it automatically delivered to the other computer and stored in a single known location on the computer.
The source computer should be able to detect all of the possible target machines on the LAN — needs to be zero configuration at the client side.
In other words, a convenient replacement for sneakernet within an office or home.