I built one at the BOL. The soil is sandy and doesn't hold moisture well and I'm not there for a week or two at a time to water.
I thought it would be a good way to have the garden water itself. It's small scale, maybe only 2 ft of wood but it will test the theory.
No verdict yet but it makes sense to me.

Perfesser, have a look at wicking beds for less watering and water retention.
http://www.internationalpreppersnetwork.net/viewtopic.php?f=46&t=856

Thanks for your sharing,
it's awesome. ❗

It is awesome, even with my heavy drought condition, my hugelbeds are my strongest producers, I have dozens of melons and tomato's coming on my main big full sun bed, and they are getting little to no extra water to do so.. we are in the process of building another 40 foot long one for next years gardening! on top of the two we already have working now.

I'm pretty happy with mine as well. Between the wood and deep layer of mulch you can see and feel the soil has more moisture in the bed. The insects are eating a lot of the leafy stuff that's there. Cabbage, collards, kohlrabi are having a tough time.
Tomatoes look great, no wilting, winter squash coming along. Amaranth is indestructible.