My RDWC Setup: (Current setup, its expanding soon)
(5) 5 gallon buckets
(1) 6 port air pump (40L per minute)
(1) 250 gallon per hour water pump
Various 1/2 water lines, return lines, fittings
(5) 6" airstones
(4) 8" deep well bucket net pots
(2) 10q bags of hydroton


Ok, first and foremost, what most places don't show you is that the drain holes all have to be level (the same distance from the ground) as your controller bucket. Otherwise you'll have improper drainage issues. Best place to put the drain hole is about 1/4" from the bottom of the bucket. Now, I've drilled 1/4" holes in the top portion (just below the lip) of all my buckets and ran air stones into it, the reason for this is to maximize air exposure to the roots in the water - This is the best way to insure good (and fast) growth.

Water doesn't spray onto my roots at any stage, my roots are 95% submerged 95% of the time. The air stones provide the needed oxygen to the roots, so I'm covered there. Now my controller bucket also has an airstone, this is more for helping me with nute exchanges than you might think, I just use the airstone in the controller bucket to help me mix in all the goodness I add. My water pump is set to go on every hour (on the hour) for 15 minutes, considering I only have about 20 gallons of water, this 15 minutes allows me to recirculate the goodness about 4 times per hour (plenty) I have my control bucket setup so that every time the pump kicks on, my hydroton is visibly wet looking at the top down (this way I know if I need to add water just by looking at my hydroton)

All this being said - If you want to constantly run your water pump (I don't) you CAN use less water, only 1 airstone, and spray the water onto the roots, however, for less money, time, and effort into parts, you can have a more rigid system.

The problems with my setup - Honestly, aside from constraint of my grow space, there isn't really any problems, it does smell like an aquarium in there, but I'm building a new carbon filter this week and that should cut the smell. I harvested my first pineapple express from this system about two weeks ago, and it was the sweetest tasting bud I've ever grown. I've got a C99 about a week or two from chop (nutes on the strains vary vastly, this is best setup for 1 strain) and the smell is just amazing (like spun sugar)

Now, traditional RDWC is setup just as I've described above. Using less water, and nozzles to spray roots is airoponics, basically your roots are always suspended in air, and then get a douse of water. I prefer it the other way, roots suspended in water, and doused in air.

Some people suggest when you setup your RDWC system that the water is 1" below your netpots, I think the water should touch your netpots, and then fill the top when it cycles (it will return to normal level after the pump is off for a few minutes) The reason I like this (as stated above) I like knowing when I need to be topped off just by looking at the hydroton, you can use a line in your controller bucket for this, but I'm actually putting a plant in my controller bucket soon