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: 126.96.36.199-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:
#### Make a backup image first
emerge -v gentoo-sources grub
cp linux/.config .config
ln -s linux-3.6.11-gentoo/ linux
cp .config linux/.
Make sure the LOG is set for netfilter
Make sure DEVTMPFS is set
Processor Type and Features -> Paravirtualized guest support -> "Y"
Hit enter, go to "Xen guest support" -> "Y"
cp arch/x86_64/boot/bzImage /boot/bzImage-3.6.11-gentoo-rscloud
cp .config /config-3.6.11-gentoo-rscloud
kernel /boot/bzImage-3.6.11-gentoo-rscloud ro console=hvc0 root=/dev/xvda1
sed -i 's/sda/xvda/' /etc/fstab
/dev/xvda1 / ext3 defaults,barrier=0 0 1
/dev/xvda2 swap swap defaults,barrier=0 0 0
h0:12345:respawn:/sbin/agetty 38400 hvc0 linux <= Add this under TERMINALS
#### contact support and request pv-grub install on image #
#### they will reboot and hopefully you'll see the new image via uname -a #
emerge -C module-init-tools
emerge -v udev virtual/udev