I've been riding for about 20 years - have a hitch (what I call it in my right leg) where my right leg (knee) dips towards the top tube. It gets worse when I'm tired. I've always attributed it to the fact that I have crushed vertebrae in my lower back and compensate for that.

So far, no knee pain - so I'm not sure about the theory that this is going to cause trouble in all people.