So udev-197 has been released as stable and in portage now. This requires a kernel config change, and if this is not in place, your server will be dead in the water. You will need to enable CONFIG_DEVTMPFS. Normally, this isn't a problem, just build a new kernel and go from there, but I have a few server images at Rackspace running Gentoo-10.1. With these older versions, updating the kernel is not that simple. If you're running Gentoo-12.3, you should be good, since Rackspace now offers kernel control with the new virtual images.
So I have Gentoo-10.1 running, which means I have the following kernel running: 18.104.22.168-rscloud. Pretty old, and everyone is pretty much using this with the 10.1 images. I wrote a procedure on how to get a new kernel so udev will be happy in this environment. Basically, it involves pv-grub, change to fstab and obviously a new kernel: