I'm one of the contributors to MythTV. While not a heavy developer, I am currently responsible for the MythFlix code as a maintainer, not author. I have contributed various small enhancements to the code over time and have been trying to also help here with the Wiki.
I currently have a multi-system setup consisting of a master backend running Redhat 9 (I know, I know) with a PVR-500 and all my storage. I have a slave backend with a PVR-150 and a remote frontend in my living room. I run SVN in production most of the time and find it very stable with a high WAF.