Very simple :
Here is the script : http://kyticka.webzdarma.cz/3d/moi/#Nudge

Purpose : To move a selected object by pressing a key of your keyboard.

Lets say you have set your Snap Distance to 1mm.

When vou press "arrow up" the selected object will move up in increments of 1mm.
When vou press "arrow down" the selected object will move down in increments of 1mm.

I find it specially helpful to move selected curve points.