Recently I came across this very tiny tool when I wanted to turn off my Ubuntu after a specific time. The software is really very easy to use and it works well with Ubuntu 11.10 as well.
EasyShutdown is a very simple skript, written in fpc, then rewritten in python. You can type in hours and minutes, and after this specific time, your Ubuntu will be shutdown. Since Natty, EasyShutdown does integrate into the Launcher-Bar. This small software has no options or configuration required. But if you would like to get an application which has some more configuration and options, there is a big brother of this app, called ComplexShutdown. ComplexShutdown supports Hibernate, Restart and Logout.