"If digital photography is your profession or passion, a color-accurate computer monitor is as important for image quality as any lens in your arsenal. If your screen isn’t a reliable indicator of the contrast, brightness, and color balance of the photos it displays, much of the control digital photography provides is lost. Fortunately, most modern, reasonable-quality monitors, whether they're a newfangled LCD type or traditional CRT, can be tuned so that they show off your digital handiwork properly. Doing so requires that you first calibrate your monitor to a standard, then profile how the monitor displays color when set to that standard. These two tasks, taken together, are often referred to as color managing your monitor".
This is a good article on everything one needs to know about callibrating your monitor. It describes Calibration and Profiling as well as advantages/disadvantages of going with just eyeballing it or using a hardware-based monitor color management package (colorimeter or spectrophotometer). One of the things this article also recommends is that "calibrating and profiling a monitor is not a one-time thing. As monitors age, their color response drifts slightly. To ensure that what you see on screen is always as accurate as possible, get in the habit of recalibrating and reprofiling your monitor about every two weeks".
Managing Color On Your Monitor
Linear Mode
