While I hate Real as much as just about everybody else, I inadvertently downloaded an RMVB file today and was pleasantly surprised at the quality vs. file size ratio. At about 70MB for a 25 minute episode, the quality was - relatively speaking - extremely good.
To quote WP:
Allegedly, RealMedia formats typically achieve much more efficient compression than MPEG-4 Part 2 codecs, such as DivX and Xvid, using compression similar to MPEG-4 Part 10 codecs, such as x264. For this reason, they have become noticeably present (though not entirely popular) on file sharing platforms such as BitTorrent, eDonkey and Gnutella.
I reckon I'm going to prefer this format for all my use-and-throw downloads.