Disclaimer - this is a bit of fun, and just looking for anecdotal 'evidence' for my theory:
I'm 16 weeks pg with baby number 3. I'm sure this is a boy for a number of reasons, one being that I'm carrying exactly the same way as with both boys (my weight and body shape has completely changed between pregnancies due to weight loss and weight gain).
I don't believe the usual theories about how one carries denoting gender, as for every 'high and at the front, must be a boy', there's someone who's carried a girl the same. However, I wonder if there are differences between pregnancies for the same woman; has anyone carried different sexes differently?