I did an upgrade from F11 to F12 x64 using the DVD on an HP S3300f.
It went fine except that the installed called my drive /dev/sde
instead of /dev/sda. It still installed Grub properly. But it had
hd(0,0) /dev/sde in /boot/grub/device.map. I believe this would have
caused problems with any upgrade to Grub.
I suspect that the problem with the drive letters was because the
desktop has a built-in USB 4 slot card reader that were labeled
/dev/sda through /dev/sdd.
Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!