I'm going to go ahead and disagree. Hung vertically, cfls or any light for that matter, produce a higher lumen footprint. There is a point where hoods are more convienent than having vertical bulbs hanging everywhere, but for most personal closet or tent grows, I'm all about vertical.
Light is emitted in all directions equally from bulbs, when you're horizontal even with a reflector you are losing lumens. If you hang your cfls vertically between and above your plants, more light from those bulbs is aimed directly at your plants. Cfls lack in penetration because your 1600 lumen 23 watt bulb is not 1600 lumens in one direction, that is total emission in all directions added up. You lose some light to the interior walls of the bulb itself even. So with that in mind, and the fact that every foot lumen footprint decreases by 75%(i.g. 1600 lumens becomes 400 lumens at a foot, then 100 lumens at 2 foot), keeping your cfls as close as possible and at the lower, middle, and upper branches is the best method for penetration and efficient lumen delivery.
I used to run a vertical 600watt tent with the plants colliseum style around the bulb and it consistantly damn near matched my friends 1000 watt standard horizontal/reflector standard style grow at harvest; and we used clones from the same mothers.