This is not a question, but I thought I would share an interesting problem/solution that I found. I'm using Centos 6.4 (runs KDE 4.3.4), on HP z820's that have Nvidia quadro 4000 cards in them. I'm using DVI cables with display port adapter dongle thingy on the video card side. DVI connector on the monitor side. I had one system that I had kickstarted and things were fine. The screen saver would start, all fine. I could unlock the screen saver. still good.
The problem arose when the monitor itself would go into power-save mode. When I would wake up the monitor, it would come on. The screen saver would display the unlock dialog, it would accept the password and unlock, but for some reason, the plasma-desktop process would stop. The desktop presented was all black with a mouse pointer (that worked), with whatever windows were open when it went to screen saver (context menus would work on windows that were open etc). if there was a terminal window open, I could run "plasma-desktop" the desktop would repaint, wall paper, widgets and all, and it would behave normally until the monitor went into power-save mode.

While it was in power-save mode, the .xsession-errors file would fill with the screen being added, then removed constantly. The Xorg.0.log file would fill with the nvidia driver initializing the monitor and enabling it "on all display devices)

It turns out I had an either old or bad displayport to DVI adapter. Once I swapped out the adapter, it behaved normally. I haven't been able to find an identical adapter in the shop so I don't know if this one is just old and not up to snuff, or if it's defective.
Kind regards.