I have a Toshiba Satellite L335. I have tested two different monitors and have the same problem. When I plug in an external monitor, I can see weird horizontal lines. I bet it's doing a super slow refresh(something like the 40-50hz) but I can't prove it. Anyway, its basically on any white area what I see is horizontal(not perfect straight, sorta diagonal too) lines. Like not really thin lines, probably 1-3mm in width(and extending across the entire screen). The lines look like not black, just slightly darker. Just subtle enough for me to notice. I've noticed that working with the screen in this state affects me with headaches and other crap to do with Over Illumination. so now it's crossed the line from annoying to I-need-to-fix-this. I've tested both monitors on a different computer and they work fine on other computers(at the same resolution and refresh rate)
Also, on one computer these monitors support a 70hz refresh rate(it runs Server 2003) but when I put it on this laptop(running Vista) it says it supports 75hz(and not 70hz) but when I go to 75hz, the monitor gives an error about unsupported resolution.
btw, both monitors are LCD and They give this flicker problem as low as 1024x900(they both go up to 1600x1200, and at 1024x768 it doesn't have this problem). The main resolution I tested with was 1280x1024