Having learned recently the importance of calibrating a computer monitor, I can't say enough to do it if you haven't done it at all and then do it routinely. After calibrating mine, with a Syper 2 Suite I discovered I have to go back about 6 months or more worth of images and correct many that are now darker than I had produced them on my Apple Cinema monitor (23").
And the changes? This image,
becomes this image.
To bad Bob Uecker was never a photographer. He'd call the old version, "Juuuust a little bit dark." So, don't be a minor league photographer, calibrate your monitor. And if your monitor can't be calibrated, get a better computer.