Okay well I will step up and say according to my wildly misogynistic, old-fashioned, caveman like approach - which I'm sure I have repeatedly proved myself to be - if I see a profile photo of a woman with low cut cleavage, and another photo of the same woman without cleavage, then I will view the photos in a different way. They will give me different impressions of the woman.
If you want to think that I'm a sexist bastard, how dare I think differently based upon how a woman dresses, then go ahead. Personally, I think I'm relatively modern and less sexist than many men out there.
But if I'm thinking that, surely other men will too. Other people on this thread and others have said they're put off men by the clothes they wear either in photos or on dates, so it's not just me, and it's not just men.
So. Dress how you want to dress in your profile photos. And maybe it's unfair, maybe it's not right, but low cut tops will, in my opinion, attract men with a certain goal and mindset.
Personally, I choose my profile photos to give a realistic impression of who I am. Me on a beach, me out with friends, me holding a fish I nursed back to life, in front of a pyramid. While riding a horse. But that's just me. I choose to portray a relatively honest impression, showing my good points, and not show a photo which I actually look really good in, because I happen to be wearing an old grungy t-shirt and it makes me look like a slob.