First off: I've only been doing this for a year. I could be back here in two weeks posting about problems, but so far, it's been great.
My duck run is filled with grass clippings and old leaves over soil. I added to it each week until it got to be 8-12 inches deep. Once full, I turn it weekly. No smells, no flies to speak of. If I see them, I turn more often.
It is a pretty generous square footage... roughly 35 sq ft per bird, and two of those are call ducks. I did that on purpose to cut down maintenance. Honestly, at this point, I can't even see the droppings build up, and they dig ALL day, pulling up worms. It's almost like an enclosed free-range/compost pile.
I was skeptical at first. Deep-litter sounds like one of those too-good-to-be -true scenarios. However, I did some research, and there's really strong research behind it offering health benefits (as opposed to just being easier). I mean by people who are looking at industrial scale set ups.
I'll repost if something bad starts happening (I hate bad advice on the Internet), but right now, I'm a satisfied non-customer of the straw dealer.