Posted about this in my blog, so I'll just put the short story here...
I've been sucking in my stomach for so long now, it's second nature. It got so bad, that I recently discovered [today in yoga] that my tightly wound stomach muscles are the reason I can't stretch properly and why I have bad posture.
So if the decision comes down to being able to stand and do yoga properly [which I love and is good for me] or sucking in my stomach to convince people I'm not as fat as I initially appear [really, who am I fooling at this weight?], I choose relaxed stomach and good posture.
So...I'm not sucking in my stomach when I walk around anymore. I already feel better, if not a little self conscious....anyone else have an experience like this?

But I think most women do...in fact I'm pretty sure I remember my mom instructing me to do so. And my flute teacher used to compliment my breathing because I wasn't afraid to stick the belly out when I breathed. She had to break most of her students of lifting their shoulders.