Just found a possible solution:

Keep the Screen on

For this, there's the little applet caffeine:

It sits in the tray, and you click it once to de-activate screen saver etc. Click it again, and it restores it. As the screenshot of its configuration shows, you can have it started automatically on login, and even deactivate the screen automatically on configured conditions (e.g. whenever playing Flash or Quake, or whenever certain programs are running). More details can be found in this article, including detailed instructions for installation and configuration.

Though the screenshots show it in Unity, it seems to work in KDE as well. I just installed it, so I cannot give reports yet (feel free to ask if you need). To install:

sudo add-apt-repository ppa:caffeine-developers/ppa

sudo apt-get update

sudo apt-get install caffeine

Again, the article speaks of Ubuntu 11.10 -- in my case, it installed smoothly on 12.04 with above 3 steps.

Power profiles

For the other stuff (power management profiles), those interested in might want to take a look at the Jupiter Applet, which offers this and, additionally, switching between different screen modes and resolutions:

This also comes in its own PPA:

sudo add-apt-repository ppa:webupd8team/jupiter

sudo apt-get update

sudo apt-get install jupiter

Those with an EeePC might add:

sudo apt-get install jupiter-support-eee