I've been enjoying streaming music to my Playstation 3 with the most excellent MediaTomb uPNP DNLA Media Server for a while. Tonight I managed to get MediaTomb to present the MythTV recordings in a format the PS3 could actually understand. I used the Cidero UPnP A/V Controller to debug the XML presented to the UPnP client by the server. Turns out the PS3 prefers video/mpeg over video/mp2p for MPEG2 video files - picky picky. Simply adding the following:

<map from="mpg" to="video/mpeg"/>

to the MediaTomb config.xml and removing/adding the recordings folder got my PS3 streaming video from MediaTomb. Excellent!