Benoît Marchal , Jul 02, 2007; 03:57 a.m.
I check the exposure through the histogram. A good histogram will match the photo, i.e. for a high-key image, it will be skewed towards the right; for low-key, towards the left. If there's a gap it must correspond to a gap in the photo.
I find it impossible to check exposure accurately by looking at the image on the camera: the screen is too small and usually too bright.