I got two Dell P2412H monitors on my PowerMac G5 yesterday and when the display goes to sleep both of them will say Entering Power Saving mode and the screen will go blank then turn back on saying the same then turn off. It stays on this cycle until I move the mouse. I do not get this issue when the a computer actually shuts off or goes to sleep.I posted this here because it seems to not be dependent on my system but a Dell-OSX thing because this gentlemen on youtube has the same issue with a monitor which is almost exactly like mine but a year older and connected to a MBP.
http://www.youtube.com/watch?v=48EFXz6xIEU
http://www.youtube.com/watch?v=48EFXz6xIEU