Great posting on Scaling in Premiere Pro CS5
If you missed Todd Kopriva’s posting on Pro Video Coalition, you should read it now:
http://provideocoalition.com/index.php/adobe/story/scaling_in_adobe_premiere_pro_cs5/
Great technical read on what algorithms are used by Premiere Pro depending on which mode (software or hardware) the Mercury Playback engine is run in.
Check it out.