Curious what the outstanding issues were, specifically. Were you able to resolve any of these in your "copious spare time" ;-)
I'm considering putting together one of these boxes. Though, being a FreeBSD person, I'm new with Linux and not even certain which distribution is most appropriate for this.
You mention MythTV can be configured to have a front- and back-end. This is probably desirable if one wants to keep a large online "library". Doing so over gig-e is probably advisable, on a NAS? I've not found any articles on this one.
I'd also be concerned about the noise factor (fans).
Thanks for a great article!