I updated my home server with the 6.4 CR packages, and I've experienced 3 or 4 hard lockups since. The server is a fanless VIA C7 "CentaurHauls" system with a 1GHz CPU underclocked to 800MHz and 1GB of RAM. It has a dual-port Intel 82546GB NIC in its single PCI slot. (It also has an on-board Realtek RTL-8110SC/8169SC NIC that is plugged in, but doesn't currently have an IP address configured.)
This server provides a number of services -- DNS, DHCP, routing between VLANs, DLNA media server, CUPS, etc. Most importantly, it runs Asterisk and manages all of the phones in the house.
There's absolutely nothing in the logs related to the lockup. The system simply becomes totally unresponsive, to the point that the console cursor stops blinking. A hard reset is required to bring it back.
kernel-2.6.32-279.22.1.el6.i686 seems to be completely stable.
I don't really expect to be able to figure this out, but I thought I'd post here to see if anyone else is experiencing anything like this with this kernel.
Thanks!