As the Fedora 18 Beta had been stable on my x86_64 test system, I decided to update the Pi from F17 to F18..   As there is no ‘update’ image available, the only way is to use YUM..    Instructions are on the Fedora site:
http://fedoraproject.org/wiki/Upgrading_Fedora_using_yum#Fedora_17_-.3E_Fedora_18
I found that the rpm –import command failed with a curl error:
# rpm –import https://fedoraproject.org/static/DE7F38BD.txt
curl: (60) Peer’s Certificate has expired.…………..etc…………
…………………………………
So… I just downloaded the key file manually, and then ran rpm –import on that local file, and it worked.

Next, I found a conflict with libxfce4menu when trying the yum update, and using –skip-broken just caused yum to loop – for several hours – before I killed it..  So, I just erased the offending rpm file:
# yum erase libxfce4menu
, and then the yum update went ahead.. and completed successfully
Then I ran # rpm –rebuilddb, as per the instructions, and the update was complete..!

Fedora release 18 (Spherical Cow)
Kernel 3.6.9-pi on an armv6l (ttyAMA0)

Robert Gadsdon.  December 10th, 2012