As a former Master Instructor and Chief of Training at the US Navy Survival, Evasion, Resistance and Escape School (SERE) in San Diego, California I know the waterboard personally and intimately. SERE staff were required to undergo the waterboard at its fullest. I was no exception. I have personally led, witnessed and supervised waterboarding of hundreds of people. It has been reported that both the Army and Navy SERE school’s interrogation manuals were used to form the interrogation techniques used by the US army and the CIA for its terror suspects. What was not mentioned in most articles was that SERE was designed to show how an evil, totalitarian enemy would use torture at the slightest whim. If this is the case, then waterboarding is unquestionably being used as a torture technique.
The full, long version of the essay is on the Small Wars Journal site HERE, and a cleaner, shorter version was published as an op-ed in the New York Daily News HERE. The op-ed hits most of the main points, but the MUCH longer essay contains a lot more pertinant information, examples from experience, and a bit more about why (besides any moral considerations - a BIG "besides") torture just don't work.
And, related, but from the Lighter Side of our Numbing of the Moral Sense Department, here's Mr. Harry Shearer with a musical look at the issue (h/t Mark Evanier):