In the classic Gnome shell, you could add an Inhibit applet to prevent the computer going to sleep. This doesn't work with Unity. Is there an alternative and just easy way to prevent the computer temporarily following sleep power options? The Inhibit panel applet was as simple as a click.
You can use caffeine. It provides an indicator which used to work on 10.10 and 10.04. However I haven't tried it on Ubuntu 11.04.
Caffeine is a nice little app indicator and does what its functions perfectly. It is lightweight and easy to install using the PPA given below. It has a intelligent screensaver/ sleep inhibiting mechanism. You can give it specific applications which while running should inhibit all power saving mechanism.
Simply to install it in Natty, open the terminal and type the following command,
Note: In the second link above, it provides a list of all the additional indicators you can install. Search for caffeine in that list. There it says it does provide support for Natty as well. However since I haven't tried it personally I cannot guarantee it.