In the world of photographic lighting tools, this might be one of the most impressive new items out there. There is another product, called RadioPopper, that does something similar (different method, same functional result) but this coming from PocketWizard is a pretty big deal.
Basically, when you take a flash off-camera, you get the benefit of much better “modeling” to the light. More shape, more natural look than a head-on flash, etc. However, you have thus far had the options of radio-based systems that can “see” around walls but give you no control once you set it at the remote location. The systems offered by Nikon and Canon do let you control the remote flashes right from the camera, and the flashes will fire exactly the amount of light that the camera says to, but those are IR systems, which require line-of-sight.
This system uses radio, and lets you do through-the-lens, “what the camera says” light output. Pretty amazing.