If having trouble with MythTV...

Just randomly try things you read on the internet until finally...

a.  your wife kicks you out; or
b. you succeed.

The last things causing me trouble were:1.  a dodgy dvd drive. Pioneer.  Can handle data, but not playing DVDs, so out it comes thanks to a good friend of the blog affording us a replacement. 

2.  Mythbackend unable to create recordings in the /myth partition on its own disk
 that I'd created, despite it being 777 permissions (read, write, execute for owner, group members, and, I thought, individuals).

Error:
2011-10-18 22:27:20.562 TFW, Error: Opening file '/myth/livetv/1002_20111018222720.mpg'.
            eno: Permission denied (13)

Solution:

sudo chown -R mythtv:mythtv /mythtv (and subordinate directories)
mythtv-setup complained that it couldn't see the directories at this point when I lazily ran it as a way of stopping and starting mythbackend.
followed by
sudo chmod 777 /myth (and subordinate directories.)

Evidently I don't know as much as I think about even the basics.

On the plus side, I found the mythbuntu builds and can update my own system .