Yep! Every day! Was at the hospital yesterday and some random asked how long I had left and said, oh you're big! To which I replied actually my midwife measured me yesterday and I'm spot on!
People find it acceptable to say these things just because you are pregnant, and it can be very insensitive!
And kirsty27, I think you're right, people don't actually know what size is 'normal' for which stage in pregnancy.
I definitely makes a difference if you are short/tall too. I measure 29 cm and I'm 5ft 1 but if someone who was 5 ft 10 measured 29cm, the bump would take up a lot less room on their body than it does on mine! xx