We are moving many systems from physical Sun Sparc machines to VMs on a 3 node Red Hat Cluster. Most are vanilla RHEL installs or vanilla with proprietary, isolated software. These VM benefit greatly from the easy auto errata update facility in the Red Hat Network.
Some systems running highly customized software from the Red Hat repositories. For example, one is a optimized NFS server. Another is a Tomcat instance with Sun Java runtime. For these systems, it would be perfect to have a way to opt-out, blacklist, or de-select in a granular way the auto errata update for NFSD, Tomcat, and Sun Java.
The automatic updates are a fantastic benefit of running RHEL. Much better than the Sun patch methods or Oracle's quarterly cluster bundles. But some of the patches can break a customized system where many configurations are made to the base software and need to be tested first.