This is probably the third time in 2-3 years that I've had an Ubuntu upgrade go bad and leave me unable to boot. Rather annoying. This time it's unable to mount my root filesystem. Last time they changed the boot loader and the old one failed to work anymore. The most annoying part is the fact that these are servers that I generally only access remotely. That's a royal PITA when it won't boot and you can no longer SSH into it.