I have 3 machines on F15 and I wanted to upgrade to F16 using yum. The first machine was flawless and am happy to report that it is now on F16.
However, I messed up on the second one by skipping a step:
To switch to grub2, run the command su -c '/sbin/grub2-mkconfig -o /boot/grub2/grub.cfg',
And I jumped straight into installing grub 2:
and now the machine boots but all I get is the prompt