I'm using the latest version of Ubuntu 11.10, and although I've disabled the lock screen options and checked the power settings, my display turns off after around ten minutes. That wouldn't be so bad, except it does it when I'm watching movies and TV shows. Is that a bug, or is there some way that I can disable that?
From the desktop, click Power Button and choose System Settings...,
Then open Screen (icon).
Under Brightness, note that the default is set to "10 minutes". You'll probably want to change it to "Never" for your situation.