I just noticed something accidentally -- apparently MythVideo can play (at least some) DVD ISO files. So, you can archive your DVDs to your file server, and play them directly with MythVideo without ripping it to mpeg4 or mpeg2.
I've been watching more and more videos through MythVideo these days, and have been frustrated with audio/video lag. I messed around with the settings and finally came up with something that seems to be working very well. Here's my new mplayer command for MythVideo: