After writing recently about my previous upgrade experience, it seems fair to report my latest upgrade experience going from F11 to F12 using pre-upgrade on the same machine at home.
Everything progressed very smoothly, even more so than last time as I'm pleased to report the bug I had written about is now fixed. Fedora now detects hardware raid devices and employs the correct work-around solution to ensure the upgrade proceeds unhindered. So far so good then and I thought I would be sailing through to another smooth upgrade. However, it appears even at Fedora 12 level there are still some small issues as it proved later in the upgrade process.
This time the upgrade was smooth right through to the end of the upgrade process, after all the packages had been installed. Just as the bootloader config was being adjusted I was presented with a rather user-unfriendly Python stack trace with an "unhandled exception" error. By switching to another console I was able to work out the upgrade had in fact completed successfully all except for the final adjustments to the grub menu and removing the pre-upgrade cache. I reported this behaviour in a new Red Hat bugzilla bug report and have been informed this bug has already been fixed upstream in Fedora development and should not occur in pre-upgrade F12 to F13, lets wait and see.
So it seems the pre-upgrade path for slightly more complicated configurations such as the one I have at home is finally starting to look good. I'm slightly disappointed it's still not quite there yet though but all things considered this was another smooth upgrade and one which someone less informed about Linux might be successful.