I have been pretty happy with my HDP, but one thing keeps nagging at me, and that is some mild banding, only on dark backgrounds with semi solid colors. I am not 100% sure it's the HDP, but I don't recall seeing it so often before I had the HDP. I have to think this is due to the 8bit r/g/b limitation, but I am not sure.
I use the HDP for two things: color adjustment for my FPJ1 projector, and CIH via shrinking option. I sometimes wonder when a projector will come out that will solve these for me, and have acceptable contrast. The Panny AE4000 is probably not there yet, but I'm thinking these requirements of mine might get there in a year or two. I would love to upgrade to a Radiance, but it will simply never happen at MSRP prices.