"I had always wondered myself why some peoples images look light or too dark online" Bear in mind (as I'm sure you know) that the Macs use a different gamma setting, by design- Mac images look dark and contrasty on a PC, PC images look light and washed-out on a Mac. But your adjustment idea is still good, some people still adjust far from the "correct" gamma. When I teach PhotoShop Advanced I do the monitor settings, but I tell my students it is a can of worms, and I am suprised how "uncalibrated" many peoples eyes are- even with me standing behind them, prompting them, they still come up with distinctly "weird" setting!