[NickW]

I also see a lot of exit pinching. What I've noticed as a beginner's symptom is usually apexing too early. Many overly enthusiastic novice drivers begin their turn in too soon. You rarely see this problem with a late apex turn in- those drivers usually have too little speed into the turn and also too much space on track out from the apex.
The other problem I see with many drivers is not getting the wheel straight early enough- or taking too much time turning.
Another symptom is the "threshold to the apex" braker who overestimates his/her traction circle, usually missing the apex completely and thus also flying off the outside of the track exit.
When I instructed (and am about to start for the Chicago region PCA soon) I used to tell students to literally try to hit every cone on the track. I would estimate how much they were off, and encourage them to really aim for the cones on the track, thus demonstrating how much they were pinching their turn in and track outs by not using the entire track.
Teaching students how to read a track is the best lesson for them.