Glad to help Jen.
It looks like the January release is in good shape. We made a last minute upgrade to the product last week which caused us to have to re-design and re-work some of the stuff we'd already done (the board design and such) - which caused a 2 to 3 week overall delay, but we're definately close. I should know actual for sure calendar dates before Christmas. We should ship by February at the very latest unless something awful happens during our last few steps and I'm pretty confident we've got everything dialed in.
I can't say enough about using the wireless already built into your flashes - you can pull off very dramatic stuff with very little thought (as far as power settings, ratios, f/stops, etc).
Try this setup to get you started......
1. Set your 580EX on your camera, and flip the little switch to "Master". Then, go into the menu and figure out how to make it "not fire" - you want to set the display so the little flash symbol doesn't show a bolt coming out of it anymore. (I shoot 550's which are slightly different - but check your manual and figure it out for yours - you're looking for "Master Emits?" or something like that. Basically, you want the on-camera flash to "command" the slave, but not actually contribute any light to the shot itself.
Note it will still flash a light that you can see - but it's quicker than a regular flash - this light doesn't add to the exposure, it's just a very fast communcation message to your slave flash - so just because it's still making bursts of light, don't let that throw you.
2. Set your 580EX II to "slave" mode - I understand you have to hold a button on the menu for 5 seconds or something for this. You could also set one of your 420's as a slave (I think they have a switch on the bottom?).
Okay, now when you shoot, you should see a very quick flash from the on-camera, and the "slave" should also fire. Once you get that, move along...
3. (assuming you're indoors, low room light) - set your camera to M mode (not the flash... just the camera, so you're setting the shutter and fstop yourself). Set your shutter to 1/50, and set your f/stop to f/4.0. Set your ISO around 400. Set your FEC to center (0).
Now shoot. You should get a perfectly exposed image with your slave being the main light source, and if you've got a bit of room light, you should see some golden color from the lamps or whatever. Pretty light huh? If you want more or less flash then use the FEC to adjust. Rule of thumb - if you're shooting at black (grey can on black sofa) - dial FEC to -1 stop. If you're shooting a white wedding cake, shoot +2/3 stop FEC.
Now move that slave all around. See what happens to the picture. Stuffed animals work great for subjects on this. Play with different types of bounce - high, low, off a wall, side, behind.... go crazy.
4. Once you figure that out a bit (I use that example first because it's easier to see what the flash is really doing).... take the next step, go outdoors in the shade in afternoon, and do some "fill" flash. Same flash setup except....
... set your camera to Av mode. Dial in f/5.6. Let it set the shutter for you.... but make sure it's not going faster than 1/250. If it is, stop down a bit, or lower the ISO, or find deeper shade. Just trust me for this example to keep it under 1/250 (and if you notice everything is studdenly "over exposed" this is probably why).
Do the same thing... except now your camera will "properly expose" the shot (f/stop vs. shutter vs. ISO) as always... but now it's going to try and "fill" the shot with a bit of flash. I always think it fills with too much flash, so just dial back your FEC a bit. I shoot around -1 to -1 2/3 for this.
Practice using a bit of light to just "kiss" the subject. You won't hardly see it - but save your mis-fires (when the slave doesn't trigger) and click between them... you'll see a dramatic difference with the flash added. Hint: Always put the fill flash on the shadow side of the subject.
Play with that a bit. Cool isn't it?
5. When you're ready to really get crazy and make your first "I can't believe it was that easy" shot.... check this out......
Find a rather bright background.. maybe a sky with some clouds. Put that behind the subject.... not directly into the sun, but something a bit bright. Now dial down your Exposure Comp (not the FEC, the *regular* exposure comp... the function of the dial without pushing the FEC button)..... Dial the EC down to about -1 to -2 (or more for more drama). This will make the background expose darker, which the camera will make up for with..... more flash. Now take your FEC and set it at +1/3.
We just told the camera to under expose the whole scene, but to add that exposure back in with flash. You should see a dramatically flash lit subject in what appears to be a strangly dark setting. I do this all the time.... LOTS and LOTS. My favorite trick. If everything keeps looking over exposed, (1/250 is blinking) then turn on High Speed Sync and try again. Nevermind why right now, just try it and see.
If those produced results for you... you're probably pretty amped about how easy it really is. All of that without even thinking of a ratio, considering power settings, what f/ value to set your flash at and the coresponding camera settings... nope. Nodda. All you have to do is memorize those two main setups in the first 2 excersises and you can do off cam flash as quick as dialing them in, and once you practice, you'll drop in and out of those settings in about 5 seconds - while talking to someone and changing memory cards at the same time.
When as many people who have discovered Actions and Lightroom Presets discover those 2 setting combos... I think the landscape of wedding photography will change in a major way. It's incredibly easy and frees you to focus on what's important in the shoot rather than piddling with settings.
Again, I'm biased, but that's why I pursued this RadioPopper concept to an obsession over the last year because it's the key to making "easy wireless flash" reliable enough to shoot constantly.
This is actually good for me also... I'm going to boil down this "recepie" to post on the RP website... more clean and concsise and with nice pictures of the display on the flash itself. I'm going to put it up as a PDF you can print and put in your camera bag. Please let me know if this is helpful.... if you try this stuff and hit snags or are confused, please let me know. I want to tailor all of the above to be as easily understandable and helpful as possible.
Good luck!!