I second this idea, having and x and y guide lines that the user can drag around would be a huge help for lining up elements.
Even better If there were two x and two y guides then the distance between the two guides could also be displayed on the status bar to aid in setting proper dimensions.
Example
So the user can click on either of the yellow lines and drag them left or right and the distance between the two yellow lines is always displayed as "X Dist = "
The user can also click on either of the red lines and drag them up or down and the distance between the two red lines will be displayed as “Y Dist =”
Just a suggestion.