It may feel good to you, but ask her first. Because if she doesn't like it, then that will be the end. But wither ask her, or sorta hit them with your elbow or something so you can feel them but she doesn't know that you are doing it on purpose.
Umm no not really, it all depends on the girl, and what she is comfortable with. Talk to her, girls love it when guys have the courage to talk to them about stuff like that. :)
If the girl knows you or she is your girlfriend of course its ok to rub a girls boob, but on the otherhand if you just met this chick at a club or something ask before touching it could really screw up your chances of getting anywhere else if you know what I mean? Some girls really like there boobs to be rubbed when kissing some don't it's a catch 22 situation really so when it doubt ask or rub her on the tummy or caress her neck.
its up to the girl.