Currently Being ModeratedSep 5, 2012 5:23 AM (in response to gavinorange)
First, you're not saving time by re-scaling in the export process (guessing that you are exporting with QT Conversion). You're adding time and (as you found out) taking a quality hit.
Second, if there are other reasons why you need to down res your movie, do it in Compressor. Use Frame Controls and set the Resize Filter to Better (at a minimum) and ideally, to Best.