LCDs have a native resolution like 1280x1024 for most 19" (4:3), 1680x1050 for most 22" (16:9).
What can happen if i use a lower one ? Obviusly the quality will be lower cause of the reduced number of pixels but will it be lower because the monitor was ment to use the native resolution ? Does using a lower resolution will make the monitor's life longer ?

Samsung says "Set the refresh rate to 60Hz. This is the optimum refresh rate for all Samsung LCD monitors.". I know that using a higher refresh rate is better for my eyes, but does it affect the quality of the image ? And how great is the life reduction ?

Thank you.

Yes, due to interpolation (guess-timating where to place the pixels).

No.

Refresh rate for LCD monitors is different than for CRT. It is the frequency at which the monitor recieves data from the video card. Images remains constant on an LCD screen until it is supposed to change. LCDs do not flicker.

Analog connections may have a refresh rate of 75hz, but many LCDs convert it back down to 60Hz. No change to life.