Flash Bracket

I'm looking for a flash bracket.
In a past life I shot a lot of weddings. My mentor always taught me that the flash head should be directly above the lens. In those days my flash head was round. Todaym most of the reasonably priced brackets, when flipped, place the rectangular flash head ( in my case 580ex ) into a vertical position as opposed to the natural horizontal position.
Does it matter if the flash head is in a vertical position ?

If you have the money check out Custom Brackets. Instead of the flash rotating your camera body rotates instead. I've been using it for the past few months and just love it. Problem is the bracket is expensive and you then need to purchase mounts for your camera and flash.

Thanks for the input berry, I appreciate the information. However, it doesn't answer my question.
Does this mean that no one who has read this thread knows whether or not the lighting will be affected if the strobe head is in the vertical position?