Havent read all the posts so i apologise if i am repeating others.

BMI (based on weight) is flawed as it doesnt take into account things such as bone density and muscle distrubution....

Just the same as labelling a weight as obese or bariatric (the medical term that is use for the really really over weight people).
I authored a hospital policy for Bariatric patients and found that a lot of places were saying that a patient over the weight of 150kg was technically Bariatric (we have not used a weight in our definition). Whilst a lot of people at this weight are very overweight, there are a minority of very tall muscle bound blokes that are this size but are certianly far from far or overweight.

I believe that if you are really serious about these things tests using calipers to measure body fat are far more effective (although so what humiliating!!!)

I too am a heavy person often weighting the same as a size 14 or 16 person, but comfortably fitting into 10-12's. when i excercise i put on muscle quickly and thus rarely loose 'weight' but certainly change shape.