well most times the origin of creation (unless you use the interactive placement for creation) is the grid's origin... when you start moving primitives before actually modifying them is when you get into trouble... after pressing insert to move your pivot point, you can hold down v to snap to a vertex and drag the pivot to a vertex at the edge of your object, leave pivot mode by pressing insert again, and then hold x to snap to the grid and move the object back to the origin.