The kerberos clock skew fixes are going to be in MIT krb5 1.11. However that release was not ready for Fedora 18. So we could run ntpdate as a temporary work around.
This is especially relevant for kickstart, as systems can come up with an invalid clock.
No longer relevant. Anaconda kickstart is being delivered in Fedora 19 which will contain the krb5 1.11 and the clock skew fixes.