Many threads, many opinions.
My experience with "standard" 2x4 rectangular "frame" lined with black plastic was, like many others, a big mess. It seems like the worst day was when I saw burners pissing in it, but the actual worst day was when packing up and knarly water was still in it,,,much of it water dumped by asshats not connected to my camp.
I use a lot of water for our camp, and have been taking a lot of the greywater back home with me, but I still like to evaporate as much as possible and have been making my "pit" on top of my van. Others are doing this on U-Haul trucks. Perhaps there is less "ground effect" playa dust to muck it up when it's elevated, but the biggest plus is that nobody messes with it...they don't even know it's there! And no camp needs it's space used by playa level evap pits. (bike around campsites Monday at exodus time and count the evap ponds that were just emptied right on the playa...)
This link https://picasaweb.google.com/DoctorIKno ... directlink
gives more info, but here are "before and after" pics from the series: