I also rode the DSB bandwagon and I had very little success with it. I was really successful at growing algae but then I've always been good at growing algae though so I can't say that it was the result of having a sandbed. However after battling dinoflagellates after a year, I restarted my tank twice. The first time was because I was using the coarser grade of sand (not the oolitic, the other stuff) and I was "supposed" to be using the oolitic, and it was "supposed" to be shallow. That would definitely cure my dino problem, it was my "old" sandbed (3 yrs old) that was causing the issues. The tank lasted 4 weeks before I could clearly see the tank was having issues again: there were incredible piles of grey detritus building up on it. Then I heard people were going without DSBs. I figured what the hell, I was almost out of the hobby anyways so I yarded that sandbed out as well.
Since that day in 2004 I have had nothing but success in keeping corals. Ya ya I've had various other issues mostly from stupidity/faulty equipment/more stupidity but my corals keep on growin after they recover from whatever stupid thing I've done to them.
I would definitely put myself in that category of people who just can't have a tank with a sandbed. I love the look but my tank would have to be a glass box full of rock and water. No corals and no fish for me to be "successful" with it.
As for the anerobic zone, some say 4 inches is enough some say 6 inches. Personally I don't think the anaerobic zone in a sandbed is "healthy" (but then again theres all sorts of critters worming around in it) and most of the nitrate reducing activities can certainly take place in the rock. And they do or my tank would be full of nitrates because my fish eat like pigs and crap like a herd of cattle
