Re: EVERYONE - lets create an HD to SD 'shimmer', 'jitter' and 'flicker' thread to end them all!!!

first, work uncompressed !

Second, the problem will stay, no matter what you'll do.
If you want a top-quality SD-movie, you'll have to make it in SD.

Something similar;
Let's say you have a nice HD-comp and use 4 pixels anti-aliasing (as in 3D apps) you'll have a nice sharp anti-aliased image. When you scale this down to SD (/5) the benefits of anti-aliasing will disappear and you'll end up with a "too sharp aliased image"
When you start working in SD, your anti-aliasing will be, and will stay 4 pixels. So Image Quality will be better than the HD-scale-down.

There's probably some nice converting software somewhere, with fancy algorithms to make high quality conversions, but it will cost you.

AE's downscaling even with PreserveEdges enabled with interlaced footage works ok but is far from perfect.
Maybe a selectable scaling algorithm like in Photoshop would be the answer but until then, using the 1 pixel blur when scaling down, is what I use the most too.

I'm still spending too much nights on doing a perfect downscale :-)

cya,

Jan