Here is a cool little trick to copy objects to sticky points on an invisible grid. Select the object you want to copy then click it's location grip. in this case the grip in the center of this circle. Then right click and pick "Copy".
Pick a point to the right to place the first copy. Now hold down the Ctrl key and move your mouse around. Notice that the circle is jumping to equal distance points as the first copy. You can place the circle as many columns or rows out as you like still hitting the even spacing, with the luxury of skipping points on the grid.
This can come in handy when laying out cubes, lights, diffusers, desks or other objects that are evenly spaced, or it just might be fun at CAD geek parties. Anyway, I know the ladies can't help but love a good CAD man.