On Xubuntu Gutsy, there is no installed tool to manage power settings. Yet the default behavior appears to be to power off monitors after a certain period of time, and this cannot be changed.
This was critical for my computer, since if my LCD is powered off, bad things happen. So I need to only use a screensaver, not to power it off.
An easy fix was to install gnome-power-manager, and then in the "screensaver settings" a button appeared to manager power settings; I then told it to NOT power off my monitor. This seems (so far) to work. (Note that I expected a menu entry for the power management gui tool, but there wasn't one. There was just the button inside screensaver preferences.)
In conclusion, perhaps Xubuntu should ship with gnome-power-manager, so that people can alter power-saving settings. As it is, it appears that there ARE power-saving settings (in particular, powering off monitors after a certain time), but these are not configurable.
I meant to say "sleep" instead of "power off", in all of the above. Sorry for any confusion. The issue is that monitors are put to sleep in Xubuntu but there is no GUI to control that.