It took me about 2 hours to auto upgrade last night from R5E50. The basic upgrade went fine. There was an error about restore and a few other things that flew by a little too quick to catch, but I just ignored all that
I stopped the install at the point where it asks to run myth-setup so I could configure my wireless NIC. That was as simple as copying /etc/network/interfaces from my backup (as madwifi is back in KM). [I started networking manually to get through the SD update.]
The SD change was extremely easy. I ran mythfilldatabase without any options and it grabbed the expected amount of data. Seemed even a little snappier than zap2it.
I always have some problems (and they are just about always the same):
Audio didn't work: ran alsaconf (sic), it detected my HW and sound worked again.
My remote didn't work. Had to modify /etc/lirc/hardware.conf and change /dev/usb/hiddev0 to /dev/lirc0 as mentioned in another thread (search for "MCE remote"). I also restored my remote config files from backup as mentioned in tjc's R5F1 Hints.
I couldn't change channels on the STB via firewire. Had to copy my modified sa3250ch executable from backup since my STB reports a different ID than the stock one (really should submit that change).
Anyway it was the smoothest upgrade yet, thanks to everyone that makes that possible.
[EDIT: that's /dev not /etc]