Note: moveAddict is no longer being actively developed.
moveAddict provides a functionality the Finder was missing, the ability to move files using the keyboard. It's meant to replace dragging and dropping for anyone that would rather use the keyboard instead of the mouse.
In a nutshell, you can use it to cut files or folders and then paste them where you want.
As a bonus, you can also use it to merge folders instead of completely replacing them, another functionality that the Finder was missing.
For anyone that hasn't used cut and paste for files before, here's a more...