Personally, I don't use MPEG-4 for safety backups. Although large, high bitrate H.264 looks very good, to my eyes it's not as good as a DVD backup and does not have equivalent navigation features. But it is all I travel with now. I keep about 20 movies on my Archos and rotate them. I archive the ones not in the current rotation on SL DVDs, which hold two to four depending on file size. Processing time is also longer in most cases to make an MPEG-4 backup vs. a DVD.