I only go braless when I sleep... for a very good reason. My b00bs are very big and I need the support. All those girls with big b00bs who are going around braless will end up in about 10 years with their b00bs hanging around their ankles.
I will also say that it's putting yourself in danger to do that. Some guys will think a girl is asking for it if she goes around not wearing underwear... true, no girl deserves to be raped but she should have the common sense to not put herself in a dangerous position.