The Screen Door effect is caused by the pixel geometry designed into the specific screen. It is much worse on some models. And for some people, it is highly annoying, while the same exact screen viewed from the same distance is not annoying to other people. It is an individual perception, but can be quantifed objectively... however no standards for it exist.
The screen door effect:
The "standard" for 5:4 LCD screens in the 17-19" range is 1280x1024... and many makers have both a 17 & 19" screen. Usually, the screen door effect is more pronounced on the 19", of the 2. Subjectively, Samsungs are often considered to be least affected by this annoyance.
Note that the screen door effect is
not necessarily affected by resolution. A 19" 800x600 screen may have no noticable effect, while a 1600x1200 can drive a graphic artist nuts. Usually though, with models of the last 6 months, a higher resolution will render this a negligible effect.
Note also that this is a huge huge issue for large screen, and projection devices. Look carefully before you buy an expensive display. Once you know about this, and other such things... and what they look like... it can be annoying forever. I often don't explicitly explain/show "average" users these and other LCD defects, especially in terms of calibration, ghosting, etc. ... its better that they are blissfully unaware, and happy with the "substandard" (by comparitive product they could have bought) device.
BTW, the pixel size can be very annoying if it is eigher "too small" or "too large" for an individual & that individual's use of the display. Large is often good for older people/those with less acute eyesight. Small is good for packing data onto the screen, but too small, and many tend to run displays at non-native resolution to avoid using a magnifying glass to see some detail/icons... which negates the advantage of crystal-sharp native resolution.
In gaming, you are forced into a higher performance video card realm, or forced to drop to lower resolutions (negating the native high-resolution of LCD). Fortunately, most action gaming is not strongly affected for average gamers, in practice... but for those that know what they look at, it can affect high-end play. For static gaming, the end effect can be "blurriness" of running at non-native resolution to match low-end graphics/CPU/RAM to high-end resolutions of newer games.
