I'm 5'11" and the BMI chart says that I must be max 178 lbs to be considered "normal". And yes, I do go by that.
From my experience, it doesn't fit everyone but I consider myself to be pretty average (certainly not super muscular -- which tends to throw off the charts). I have been between 170 and 180 where I *FELT* normal.
Even though I'm over 180 right now, I definately don't feel or look overweight but it's still too big for my own comfort.
As for the lower weights of the BMI, they make me far more nervous then the higher weights. I know that if I were to fall below 150 lbs I would at the very minimum lose my shape and any more lower would look sickly -- which may work out great for all those supermodels out there that are airbrushed -- but I would not be comfortable with it in my real life unless I was super fitness woman and super healthy about it.
So really, a goal weight is just a number that is subject to be modified as time goes on. When I first started, it was 180. Then it changed to 170, and my secret number is 160. You'll know as you go.
