.....*off topic-ish* And LCDs can get burn in, I've got a taskbar burned into the top of the screen from when i used to have it up there. Or it could be a window bar from something maximised...
I didn't realise that some people still had a problem with this, even on LCDs.
I've just done a bit of Googling & come back with this ;
"LCDs do not burn in like a CRT or plasma display can.
However, there is an effect called 'image sticking' If an image is left on the screen for a long time - tens of hours - then when the image is changed there may be a inverted shadow of the original image left.
This is due to the collection of charge in the LCD panel from the static image. It is usually worse for IPS and VA technologies, and not so bad for TN. It also depends on the purity of the liquid crystal material, so there can be some panel to panel variation.
The big difference between 'image sticking' and 'screen burn' is that image sticking will fade away after some time and the panel will look normal again. Once a CRT or plasma has the phosphor burnt then nothing will remove that image from the screen."
Also this longer article, which includes info on how to fix your problem, kieran5676 ; http://compreviews.about.com/od/monitors/a/LCDBurnIn.htm
I may have to re-think my use of screensavers!
I don't have a screen saver, after reading your comment I re-enabled it. I don't know if this affects me but I have a TFT Flat Panel, and not LCD.