10.20
After much delay, the Caffeine developers are pleased to announce the 1.0 release of Caffeine, an applet that disables the sleep and power saving modes of your Linux system. Version 1.0 adds one BIG feature:
Automatically activate for user specified programs.
Some applications like games, fullscreen or not, take mouse and keyboard input but don’t prevent the screen-saving and sleep modes.
Instead of having to click on the icon before playing games, Caffeine 1.0 automatically activates for any process you want.
Adding processes to activate for is easy, since the dialog shows both running and recently running programs, which makes it feasible for you to add fullscreen applications to the list.
As you could see in the first screenshot, Caffeine can also activate when the user is playing Flash video or playing Quake Live. Flash video detection is not perfect but it detects most popular flash video players including YouTube. Unfortunately, we haven’t found a way to detect if the user is playing a video on Hulu.com, the workaround is to use the hulu desktop client and then add that to the list of programs to activate for.
Quake Live does not run as a separate process so it can’t be detected the normal way, but fellow Caffeine developer Brad Smith and myself both play Quake Live so we really wanted a way to do this. What I came up with was iterating through each X window using python-xlib and looking for a window named “QuakeLive”.
Because of all these features, you will probably never have to manually activate caffeine again. 
1.0 has also been translated into many more languages than the previous release. Unfortunately, most of these translations are not yet complete, but if you want to help translate head over to the translation page.
Installing
The recommended way to install Caffeine is from the Personal Package Archive (PPA): https://launchpad.net/~caffeine-developers/+archive/ppa
sudo add-apt-repository ppa:caffeine-developersAlternately you can grab a deb or tarball from the Launchpad download page: https://launchpad.net/caffeine/+download.
[...] for which this won’t work, like hulu.com (a workaround for this issue is available; see Isaiah’s post for [...]
[...] UPDATE: Caffeine 1.0 is out, read the details. [...]