I have been a long-time advocate of the Nikon CLS flash lighting system, and find its ability to painlessly light a scene using multiple off-camera flashes to be a real help, especially in ad-hoc shooting situations. This is never more so where time is at a premium, and you don't have the ability to wander around endlessly manually updating power levels on individual flashes. Of course, you can stick an SB-800 or SB-900 on top of the camera to act as a master flash (which is really a waste of a flash), or you can use the built-in flash on a supporting camera body. However, I find that the preflash of the flash on camera tends to make a portrait subject blink at just the wrong second before the main exposure is made, giving you squinting subjects as often as not. Not ideal. It is because of this that I finally decided to purchase an SU-800. Not only does it communicate with the remote flashes using an almost invisible infra-red signal, but it also has a built in focus assist lamp, which is much less bright than the white light a camera body emits, again making the subject much less likely to blink at the wrong moment. With the SU-800, you can control the output of up to 3 separate banks of Nikon flashes without moving from the spot, either in CLS or manual modes. This is to me preferable to the alternative of using Pocket Wizards, which require the flashes to be individually adjusted by hand. The only limitation with the SU-800 is that it requires that the remote flashes can 'see' the infra-red signal, which really means shooting indoors in an enclosed environment, or having the remote flashes in a fairly close proximity outdoors. Being radio driven would remove this limitation, but flashes do tend to emit a lot of electronic noise, so introducing radio control as part of a TTL metering based flash system is not a trivial, as Pocket Wizard have recently found to their cost with their new Canon TTL based system. Given the range limitation, the SU-800 is an excellent solution to off camera remote flash with full CLS support. Its only flaw is a relatively limited range, so 4 points. Highly recommended.