WARNING: Do not upgrade to CentOS v6 kernel 2.6.32-431.1.2.el6.x86_64

WARNING: Do not upgrade to CentOS v6 kernel 2.6.32-431.1.2.el6.x86_64

It can render your server unbootable:
http://bugs.centos.org/view.php?id=6831

I had to rescue several servers within a few minutes this morning. You need to reboot from the previously installed kernel via the console and modify your boot loader not to use this new kernel and wait for a replacement from CentOS. Nasty.