When you're deciding on the details of your outdoor ceremony there's something you may not have taken into consideration...the lighting!  The lighting is extremely important not only for the photographs but also the guests and even the couple.  Too often I see shadows on the couple, or worse yet just on one or the other.  I've seen couples crying, not from emotion but from having to stare into the sun.  I've seen guests, blinded not by the beauty of the bride but the glaring sun right in their faces.  The best thing you can do is to try and orient the ceremony so that the entire bridal party is evenly lit by the sun and the guests have their backs to it.  Don't stand directly under a gazebo or tree unless you can ensure even shade throughout.