In response to John's posting http://www.zimbra.com/forums/announc...html#post72028 :-
CentOS uses the upstream sources from RH, and as long as you stick to the base and not use the CentOS-Plus packages it is completely compatible with RH.
So with respect to the Scalar::Util problem I cannot see how it was CentOS that caused the issue ? If that was the case then why has Scalar::Util been distributed with the RHEL4 GA 5 release
IMHO it is a bit misleading to say CentOS caused the issue, and yes I do also appreciate that CentOS is not officially supported, but neither is Gentoo. At least though CentOS is compiled from Enterprise class sources, unlink Ubuntu which does not really have that presence yet.