Our big stumbling point appears to be RHEL 5 and Kerberos root users. 
Specifically - RHEL5 hardcodes 'nfs' as a service principal to be used by 'root' for accessing an NFS mount.

We've been looking at various different solutions, like creating an NFS user with uid 0, or (somehow) trying to map nfs <=> root on the filer. 
But was wondering - does anyone have a kerberized RHEL 5 environment? How are you handling root access?

We've got RHEL 6 sorted, probably, because it looks like you can simply cut down your keytab to have 'just' root, which is then used for mounting/access etc.