Another CM lifer here!! I love CM.
Kat - I did take one of their classes, but I did realize that what I always thought of as a "good" photo is, in most cases, definitely NOT considered a good photo in true photography standards. So I really tried to develop my eye for a great photo by reading their "Serious Critique" section. Limb chops: bad. proper exposure: a MUST. complete, almost unreal crisp focus: a MUST.
The benefit of watching the serious critique thread is that people asking for feedback are required to give their settings for the shot. I learned a lot in the beginning from the group's feedback on what should have been different in the camera settings (ISO, shutter speed, aperture).
The single most common issues are:
not keeping shutter speed high enough. Most of us here are chasing kids around, which means that they're always moving. Keep your shutter speed over 200, which means increasing your ISO or opening your aperture (making the number lower) to get enough light.
Not using the right aperture. Once people start getting more expensive equipment (even the "nifty 50" - the $100 lens) - they're tempted to use an open aperture (low number, like 1.8) for portraits. It is VERY DIFFICULT to get good focus at these aperture settings - the focal plan is tiny and the photo won't be "great" unless it's right on the eye(s).
You'll see lots of great examples of this on that thread, and eventually you'll start to see them yourself as soon as people post them!