Good question, but there is something you're not getting. Unless you're talking about the new PocketWizard E-TTL system (Mini TT-1 and Flex TT5), it's two quite different systems. The ST-E2 is a "wireless controller" that works with some Canon flashes (and some Sigma flashes, like the 500 DG Super). It acts much like a 580EX attached to your camera. (In fact, you can use a 580EX that way, turning off its own flash.) It exchanges exposure settings with the remote flashes. It can work very well. (Note the conditional phrase.)


But--and this is a big "but"--it has major limitations that can make a wireless set-up difficult or even impossible.


1. The flashes have to "see" the ST-E2 signals. Their sensors have to FACE the ST-E2 for best results. IF you're in a small room, the ST-E2's infrared signal can bounce off walls, but that reduces the range and reliability. Otherwise, you'll have to turn the flash bodies so that they face the ST-E2's location, then turn the heads in the direction you need


2. For the same reason, it's difficult to set up a wireless network with umbrellas, though you can turn the cold shoe on the umbrella bracket around so that the flash sensor faces away from the umbrella. Even then, though, they probably won't directly face the camera. It's even more difficult to do a wireless set-up with softboxes, scrims, and other modifiers that block the flash sensor.


3. A ST-E2 (or 580EX/580EX II) controlled network is even more problematic outdoors. If you're shooting in the daytime, using fill flash, you can probably forget about a wireless network--you'll have the proverbial slim and no chances.


4. Wireless networks are notoriously unreliable--thepercentage of mis-fires can be quite high unless you're in optimal conditions.


5. To make matters worse, the ST-E2 uses an odd battery (2CR5) that can be hard to find and is not cheap. When I got mine, I tried to find a battery locally. One (of three) Radio Shack store had one for something like $20+. Finally, I found one at Best Buy for about $13. (I later ordered two from an eBay seller for $5 each with free shipping. B&H has them for $6 plus shipping.) That's a far cry from AA alkalines that the PocketWizards use.


The PocketWizard (PW) Plus transceivers, on the other hand, are wireless remote triggers. They don't support E-TTL. Their job is to transmit and receive a simple radio signal that tells the remote flash(es) to fire. The lack of TTL is the obvious disadvantage (that also means no high-speed sync) but the advantages are significant:


1. Much longer range--up to 300 ft in the best circumstances, vs maybe 20 ft for the ST-E2. I've gotten at least 180 ft.


2. Line-of-sight is not required. The remote flash can be behind a wall, for example, or behind the camera--almost anywhere. (Some indoor sports photographers put flashes up above the arena/court, firing down, for example.)


3. Works outdoors as well as indoors.


4. Much more reliable--not 100%, but pretty close, depending upon the distance.


5. Works with umbrellas, softboxes, etc. (Some studio lights have a PocketWizard receiver built-in.)


6. The PocketWizards can actuate a camera, as well as the flash(es) for a totally remote setup. (That will require one more PocketWizard unit, of course.) I have 3 PW Plus II transceivers and one transmitter (no longer made--I got all 4 on eBay). I can put a transceiver on the camera hot shoe, set it to channel 1, and connect the "Camera/Flash" jack to the camera's remote trigger connection through a special cable. The PWs for the flash(es) on channel 2. I carry the PW transmitter set to channel 1. When I push the trigger button, the PW transceiver on the camera fires the camera shutter, then, when it gets the signal through the hot shoe, it transmits a "fire" command on the next channel up (2) for the flashes.


7. You don't have to mount the PW on the camera hot shoe. You can connect it (with the right cable) to the camera's PC connector (if it has one). That way, you can also have a flash on the camera (or on a bracket, using the off-camera cord). Later today, I'll try to take a photo of my 30D + Really Right Stuff Wedding Pro Flash bracket + 580EX + PW transceiver and a set-up without the bracket to show what I mean.


For more on using off-camera flash, go to the "Strobist" site. There are tutorials, articles, and discussions.