I used mine very successfully on a D300 (DX). However to get Autofocus on DX you are restricted to a camera body that has the AF motor built in to the body....These are D50, D70, D80, D90, D200, D300, D300s and D7000.
The D3x00 and D5x00 and older D40, D60 bodies do not have the mechanical AF drive.
My copy of the lens has a moderate fall-off in sharpness after about 330mm wide open but at 400mm and F7.1 it is very sharp. the main reason why people say it isn't sharp is because it is light enough for hand held use and due to the long focal length it needs to be used with very high shutter speeds for best results. I always try to shoot at 1/800 or faster.
Currently, the sigma 150-500 OS offers similar optical performance (according to reviews) but is much cheaper and has the faster electronic focus. I have two friends with the Sigma lens...and based on their results I think my 80-400 is a little sharper and a lot more contrasty.