If you shot in RAW, you could easiliy readjust the exposure in post processing and completely "save" / make perfect (at least the exposure of) the image.
I strongly recommend a monitor calibration tool. I use Spyder 3Pro. That way I know at least I am producing images with a reasonable range of brightness / intensity / exposure. There's no guarantee that the viewer will have a decently accurate / calibrated monitor, but that's their issue.