I thought for a while of making the subject of this response "Dan vs. Dan: Point/Counterpoint,"
Here's my take on this: Your mileage may vary.
Cracking AGAINST the natural curve of the whip, (i.e. as Adam Winrich rightly put it, "Belly Up,") is the method used by many whip crackers, particularly Hollywood Stuntman and Fight Coordinator, Anthony DeLongis. He uses this method to slow the whip down somewhat and make it's movement easier to photograph, (he has a point, though I have proof that it's not necessary, and will hopefully prove it further in the next few months. But then, I also believe that the camera must be able to cross both fire and water... So I have far more faith in the medium.)
It also "telegraphs" it somewhat for stage and theater work. This works well, as while you can slow down a sword on stage and make it look good, it's a little more difficult to slow down a whip, which is inherantly designed to be supersonic. Slow and steady. Good plan for theatrical work. This method also doesn't concentrate as much energy into the whip, which is an important thing when hits and wraps have to be performed by actors who are not incredibly experienced with the whip.
For more on this, read Anthony DeLongis's article "Faster Than a Speeding Bullet: The Ultimate Flexible Weapon" on the "Latigo y Daga" site, here:
http://www.filipinofightingwhip.blogspot.com/
Now, when I first read this, my response was, "What the heck is this guy thinking?" but I have come to understand what he's getting at. While I am still no great proponant of this method, I am quite capable of cracking like this and plan to occasionally use it myself.
The OPPOSITE method, which I prefer to see and prefer to utilize myself, has the whip thrown spine up. This method uses the whip's natural curve to help accelerate it faster. The whip wants to curl under, and the normal method of throwing helps it do that. This method focuses more energy into the whip, make it's crack faster, (and louder, as Delongis mentions,) by focusing the energy of the wave into the tip of the whip.
It is this process that makes the whip naturally roll out and go supersonic. It is this process that gives a narrow strip of leather with a fluffy piece of baling twine on the end the ability to slice through flesh as easily as a scalpel and shatter bones as easily as a hammer.
Likewise, I find that throwing whips in this manner keeps the transition area above the handle good and tight which aids in the accuracy and ease of cracking for the whip. All of the Aussies I know throw whips this way. All the WWAC competitors I know throw whips in this way. All the martial artists I know throw whips in this way.
Cracking in this manner is, I think, the most beautiful expression of power, grace, energy transfer, and kinetic beauty that can be experienced.
But it all boils down to priorities. My priority when I crack a whip is often to feel first hand the power, beauty, and perfect "Zen" feeling of cause and effect, leverage, and wave mechanics that is whip cracking.
Anthony DeLongis's priority is to capture that same feeling, but in such a way that it is safe for everyone involved, (which otherwise, it wouldn't be. ANYTHING accelerated past 700 MPH is potentially deadly!) After reading DeLongis's article, I had my wife watch me throw a whip both ways, and she couldn't tell a difference. And it was noticably slower to me, (the thrower,) and had FAR less energy in the fall when it cracked. I can tell the difference on screen and off. But I crack whips a lot, and I edit video for a living, (and tend to pick out @#$% from single frames of video zipping by at 30 frames/second. It's a curse. Really.)
I see why he does it. Just prefer the look, feel and resultant way the whip breaks in from the "Spine Up" method.
My two cents. Sorry if I ramble, It's been a long day, and I'm pretty tired.
-Dan