My frist wierd cultural boob experience (I haven't had nearly enough of them) was in Caines, Australia. Some friends and I were there for a few days and some of the girls I was with wanted to go down to the Public Lagoon area to lay out and some of the guys thought it would be fun to get some beef from the store and BBQ it (endless shrimp on the barbie jokes were made cause it's Australia hurr). I was talking to my friend Jule while she was laying out, and for some reason, she sat up to say something to me, and her shoulder/head perfectly framed a girl laying out topless behind her. It threw me for a second, but after looking around, I realized lots of girls were doing it, so it was just a thing, and no big deal. I, of course, asked Julie if she would be doing it, and she hit me.
But, boobs have never really been a big thing to me. There have been numerous occasions where I've befriended a girl, decided I liked her, then someone pointed out to me that she "has a totally huge rack, man" and it's hard to get someone to believe that I just never noticed it before they mentioned it. I'm way more of a butt guy, but apparently there's no such thing as a guy that doesn't like boobs, according to most of the people I know...
Like Narr said, they can definitely be great in certain circumstances, but they aren't the kind of thing I really look for, because... well, it just never really has been. I don't actually have a reason why.