Thanks for all the replies. I guess this QR system wouldn't have become a de facto standard if it didn't offer tangible advantages. I think I'll go for it (once I manage to decide between the K-20x and the K-30x).
Along with security and speed, another those advantage to the Arca-Swiss open channel dovetail design is it's versatility. More than just a way to attach a camera and lens to a tripod head, Given the variety of rails, bars, additional clamps (panning , cross angle and parallel to rail/bar,) and rotators available from different manufacturers it can be a way to securely place a camera where a standard support system won't work or fit. I think of it as being a Erector set for photographers and videographers.
