I know what a screensaver is.

Just never heard of ghosting (as MMZ nicely put it). We still have a few 14" oldies (including a smaller 13" black and white monitor for the novell server). Never seen those events (and those were abused monitors).
I know the phosphorus layer does get "yellow" by usage (and age), and starts loosing brightness, but never actually heard of the cathode burning an image on the layer (doesnt it have to damage the colour grid too?...) .
Always thought that the cathode didnt have enough power for that.
Anyway, sounds a nice thing to have on display (pun intended).