I've been going to a yoga class once a week for the last nine months or so. I guess I'm lucky that I have a very gentle instructor who repeats something like this many times in each class: "let go of any preconceived notions and judgments of what you should be doing and pay attention to yourself". I've stopped looking around the room to see what others are doing and just try to push myself a bit more each week. Its been slow but I think its paying off.
Problem is, some limits are hard to detect until you've exceeded them; "listen to your body" really must be augmented by details and rigor around safe progressions through the practice (which, to complicate things, obviously vary by individual).
Also, there are some limits that should not be exceeded, period. Like the cases in the article where they exceeded the operating tolerances of the neck and gave themselves strokes.
Yoga certifications really ought to include a basic anatomy and physiology component.
