I setup a 20 gallon long barebottom back in September. It's a zoa tank, and I didn't want to worry about the flow from my MP10 pushing around sand and/or burying recently cut frags...the other reason I went with it is because it makes removing detritus simple. I've found 2 areas on the bottom of the tank where sediment starts to settle, and just vacuum it out every week with my water change.
I like the simplicity and the lack of areas for detritus to hide and accumulate in such a small system. It does limit livestock choices, but I opted to go with just a single fish in that tank (pygmy angel) and had no real need for a sandbed. As far as looks go, my tank was placed on a table with a gray ceramic tile top, so it didn't look too bad initially, and I'm starting to see coralline algae cover the bottom of the tank. It looked odd at first with rock and no sand, but the clean look grew on me...I'm considering going with a barebottom tank again if I do a larger build, and would probably just run a sandbed in my fuge for additional filtration and buffering.