Using Premier Pro -- Recently upgraded to CS4. When exporting sequence to a quicktime movie using the Adobe Media Encoder - all settings are same as (equivalent to) what I used to do in CS3, but the result is pixelated, or posterized. See samples of what I am getting, over here: http://www.tamotion.com/sample/Picture11.png and http://www.tamotion.com/sample/Picture12.png
I am getting the same result on 3 different intel iMacs, all running Leopard 10.5.5, 4GIG RAM (in one case, 3GIG), so the problem is not specific to any one machine. I assume there is a basic setting I may have overlooked.
You need to set Bitrate in AME (it's turned off in default, don't know why it's off).
I had this problem too, but with switching on Bitrate and set the correct number - this correct problem with low quality mov's for me.