I don't like cleavage if it's overdone and obviously a cry for attention. But typically, I don't mind cleavage that is tastefully displayed and compliments the woman overall. I do have one friend who shows her cleavage every day, in any circumstance... I mean, for professional meetings and presentations, this girl STILL wears low-cut and tight shirts and pants. It takes away completely from people's professional treatment of her, but in some ways I think she doesn't mind... she just really thrives on male attention. It's unfortunate.
For me, I usually only display my best cleavage around my boyfriend... and I don't mind doing so in public, when he's around. I like knowing that while others look, only he can touch... and I love it when he ogles me across the table.
If he's not around, I'll wear something flattering (I do like the way my boobs look under a shirt), but I will make it much more subtle. No gaping v-necks. I like feeling pretty, but the only person I want unashamedly lusting after me is my boyfriend.
Now, if I'm going to school or doing something for work, etc... I tend to dress a little more conservatively (enough that I won't get stared at). This is especially true if I am going to be meeting a guy one-on-one (e.g. my advisor, my therapist, an undergrad student, etc)... I wear loose t-shirts, non-fitted pants, light jackets that cover my boob shape, etc. I HATE the whole eyes-glancing-down thing. It makes me want to punch a guy if he does that when we are supposed to be professional and doing business, etc. (And yes, men out there, believe me... no matter how quickly you think you're doing it, we notice. Every time.)