One of the problems users are facing, without any clue about it is that there screen gets locked after a certain time and they can't find any option to change it under Power Settings or Screen Saver settings. In fact there is no screen saver settings.
However, there is a way to disable automatic screen lock in Ubuntu 11.10.
How To Disable Screen Lock
Go to System Settings on the top panel and then click on 'screen' option.
Here you will see two options:
1. Turn off the screen after a given period
2. Lock the screen. This is the option you are interested in. If you want to disable the automatic lock, then slide the lock to the 'off' position. Now, your screen will never get locked.
Source: http://www.muktware.com/man/2720