Thanks Paul. I also did a search and came up with this:
Originally posted by Bob Pariseau
"Macroblocking is a type of over-compression problem that can be found using any player on some commercial DVDs where the producers weren't careful enough when they made the DVD transfer.
The "Macroblocking Bug", on the other hand, is a bug in some players that causes video noise to be emphasized, and is usually first seen as what appears to be excessive macroblocking noise, even though the same scenes play just fine on other players.
So most players will exhibit macroblocking if you play a poorly produced DVD. And some displays will emphasize minor, thoroughly ignorable, macroblocking typically found on mid-quality DVDs if the display is not correctly calibrated. The point being that just because you see "macroblocking" does not necessarily mean you are seeing the "macroblocking bug".
Players with the bug -- players that exhibit the problem even with good DVDs and well calibrated displays -- appear to be limited to players using a particular Faroudja video chip. For reasons not clearly understood, not all people who have these players see this problem. It may be related to an interaction between the damage the player is doing to the image and subsequent display-dependent processing such as scaling going on in particular displays -- processing that would be done differently or not at all on some other display. It may simply be that the bug appears only in a fraction of the units manufactured. No one seems to know for sure. The point being that there are many happy owners of the players that are known to have exhibited this bug in someone else's setup.
Even in players which are known to have the bug, the problem does not appear if you use 480i output. The Denon 3910 shows the problem on it's Component 480p outputs but is almost entirely free of it at one specific resolution on it's digital outputs. Thus depending upon your intended use, even a player with the bug may work just fine for you even if you have the type of display that seems to make the bug visible.
However, players without this particular Faroudja processing do not appear to exhibit the bug with any displays at any resolution using any cabling. The Pioneer Elite 59avi, for example, appears to be free of this problem."