In terms of the definitions accepted by most civil societies and explicitly stated in the Geneva Conventions, I think the act of torture has been used by the administration.

It is very difficult, however, to argue that the U.S. does not torture. As has been mentioned, most of the interrogation methods used are secret, and by Executive Privilege(as nebulous a legal principle as any), are completely shielded from congressional or judicial review.

One can only argue that the common definitions of torture are too strict, and there isn't a lot of room to argue on that point without getting into meaningless hypothetical cases.

I think torture should be strictly defined for just this reason. It is far better to quench the temptation to use violent or abusive interrogation techniques than to deal with the grave consequences of not doing so.