Well, having spent years editing SD projects in the DV codec I know that SD stuff not only takes less hard drive space but also renders and exports WAY faster and I miss the speed. I just don’t see the point of editing HD only to output to DVD each and every time.
A recent wedding project (all in HD) took up over 200gb of hard drive space and took HOURS to export from the timeline to a self-contained Quicktime file….when the same project in SD probably would have been less than 100gb of disc space and exported in like 45 minutes.