I have a server that is running centos 5.3 x86_64 that until last week was running fine. With no error messages in console and in /var/log/messages the server simply stops responding.
I posted the following bug to RedHat yesterday for similar symptoms with RHEL 5.4, same kernel. https://bugzilla.redhat.com/show_bug.cgi?id=525898
I happen to have a 3ware raid card, but didn't think of it as a culprit. Were you seeing any soft lockup messages with kswapd0 in /var/log/messages?