You now have to play about with the quality settings in your desired codec.
http://www.warcraftmovies.com/movieview.php?id=70981 - Has a few good tutorials as do the stickies in this forum. :p
Just as an example...
Currently I have to produce and get published Sunwell kill movies fast after receiving footage from 3/4 other guild members. Now my computer is decent but not state of the art, if I had more time I would use the x264 codec, but seeing as I don't I encode as WMV (Windows Media Videa V9). Usually I set the quality level to anything between 90-93%. Bare in mind WMV produces a thin veneer (your average joe won't see the difference) over your movie, so is sometimes not the preferred codec for machinima makers.