I am running CentoOS 6.3 and have set up a local nameserver. As a result, I’ve customized my version of /etc/resolv.conf to include both the IP of my local nameserver as well as a domain and search configuration directives.
When I restarted the machine, or if I restarted networking resolv.conf was overwritten.
It turns out that the contents of the ifcfg-ethN files determine how the network scripts behave and how, or if resolv.conf is modified programatically.
To prevent this make sure NOT to include a DNS1 (or 2, etc) entry in your ifcfg file and make sure TO include a PEERDNS=no entry.