After upgrading from RH 6.0 to 6.2, my monitor no longer enters suspend mode. I have made sure that "Option power_saver" is in my XF86Config. When I try "xset dpms force suspend", the screen flashes black for about 1/10th of a second and then returns to normal. I have an Intergraph Intense3D (Alliance Promotion + Voodoo Rush) video card and am running XFree86-3.3.6-20 in 16bpp mode.
I rebooted and that did not fix it. However, booting into Win98 and forcing the monitor into suspend mode followed by booting into Linux seems to have worked.
this is a very hardware specific bug, we do not have the hardware in house to analyze the problem in depth. Likely not to be fixed.