I was under the mistaken impression that I'd correctly calibrated my monitor around the time I first started painting digitally, over a year ago. Now I've realized that the calibration was off. After re-calibrating, I'm finding every one of my paintings looking too dark--easily corrected using Levels, but that takes time. Furthermore, I'm used to using colors that looked right on my uncalibrated monitor. Now that I've got this monitor set correctly, those colors don't look right. I have to re-learn which colors I like to use.
Now, I'm not saying this to complain. I'm saying this to remind anyone and everyone not to make my mistake! Calibrate your monitor(s) and do it right. I found this page (http://epaperpress.com/monitorcal/) and this page (http://www.normankoren.com/makingfineprints1A.html) helpful.
Seriously. Stop reading and calibrate. Right now!