You can use the symmetry tool for precision centering of stencils. Just have the "Show Symmetry Control" unchecked and you now have the center of you page marked with the segment lines. You can place the end of the pin where the lines cross. Use the arrow keys for small movements. You can even move the center of the symmetry tool to a precise location so you can use it to place stencils any where you want on your canvas and know exactly where it is. So with a little math you can align and distribute stencils and not just eyeball it. The more you zoom in the more precise you can get.
I have made grids and stencils with registration marks in my vector drawing program (CorelDraw) to address this problem before, now I can do it quickly with the Symmetry tool.
Thanks ArtRage team!
I made this photo card frame aligning my stencil with the Symmetry Tool.
The background tile was made with the Symmetry tool and applied with the pattern fill.