Remember to ungroup everything on your page before sending it. Having everything grouped will often create postscript errors or result in elements dropping out.
Keep in mind, If a grouped object is placed on top of another. It will make all of the objects in the group on top of the underlying objects. Having many sub layers in a design element can make imaging complex files difficult. By ungrouping your creations the imagesetter will have less work to do. Meaning faster more reliable film output..