I have trained the family to zoom 4:3 (usually SD) content with # button. Yes, it gets close to chopping some heads, but we are used to it. Fortunately, we hardly ever record any 4:3 content these days. This way, it doesn't matter what color the bars are because these don't appear.
Personally, I think it's ok to watch a little 4:3 content on plasma, AS LONG AS you watch an hour or so of 16:9 or WideScreen content afterwards. This helps to exercise all the pixels and even out any IR. If someone goes crazy with the 4:3, run the horizontal white bar thingy before turning the TV off. Also, be sure the "auto shift pixels" option is on.
Thanks for the heads up on the AutoHD feature ... I didn't even know we had that now. We got the "Black Guide update" a couple of weeks ago, so I'll have to see if I can find it.
For those that don't want to use the Zoom button, and choose to"stretch" the non-HD content for non-HD stations only. Go under Settings, and you can set your Display to "Stretch." In this regard, all non-HD stations will fill the screen on a 16x9 HD set with proper HDMI or Component Cables.
HD stations that show SD content will always have the side-bars and can not be changed.