A few hours ago, I tried upgrade using the DVD, and it was apparently unable to use Mageia's mirror list to get a
FULLY UP-TO-DATE mirror. It proceeded to try and upgrade using just 'core' and 'nonfree' from the DVD, and failed to complete.
I switched to the command-line 'online upgrade' process. I chose to use 'mirrors.kernel.org' as media sources, they seemed to be complete (and very fast). "urpmi --replacefiles --auto-update --auto" wrestled with about 2100 RPMs on the first round (i have a very 'fat' box), but didn't find additional RPMs when I repeated immediately. It also didn't find any addtional RPMs following restart. Although those 2nd and 3rd re-runs have been necessary in the past (Mga2 -> Mga3, the very first command found ALL of the RPMs in this upgrade.
I've not tried any of my alternate DE's yet, but the upgraded KDE desktop works perfectly. It "feels" a bit faster, too. I'm delighted by the simplicity and relative safety of the command-line upgrade.

absolutely flawless, but you do need a good netowrk connection.