I have a feeling this thread may explode.
Did any else get weirded out by the pregnancy comment? That made no sense to me. Why would it be proper for a pregnant woman to show off her engorged tits if it's inappropriate for other women to do so? That's just strange.
I have rather large assets and it is sometimes hard to keep them hidden. Normally, I don't give a shit. However, I work for a male lawyer, so I would feel very self conscious parading into the office with a low cut top. Low cut, for me, can seriously lead to spillage. Sure, I'd love to wear whatever I want, but the reality is it's awkward. I'd rather just wear high-necked tops than endure that.
So I'd say, depends on the work place. If I worked with just a bunch of people my age, I wouldn't be too concerned.
And I can't really blame men for looking, I have a really hard time not glancing at women's cleavage too, because it is so THERE and so near their faces. I have to make myself focus on their eyes.

I don't really care if men/women look at mine, but if its my old man boss, it's just awkward.