It would be real nice to have a Quick Preset for converting videos into a format which is compatible with ReplayTV. The doc that comes with rtvtools says that compatible "MPEG-2 files should have the following attributes:

Resolution: any valid MPEG-2 width, 480+ height
Framerate: 23.976, 29.97 and 59.94
Bitrate: 2-8Mpbs CBR/VBR
Audio: 48KHz @ 112-320kbps, MPEG-1 layer II
GOP struct: 1 seq per GOP"

I often use ffmpegX for this very purpose, manually setting the bitrates, framerates, padding (if aspect is not 4:3), etc, so I know ffmpegX can do it, but if ffmpegX can figure out all the proper tunables by itself, it'll be useful to a lot more casual ReplayTV users.