I can't really think of any offhand, but sometimes if a girl already has fairly large breasts, it's easier to hide an implant. But even then, many people can tell because we're all such breasts experts, heh.
I used to not mind them so much until I did a binge of strip clubbing a few years back. There is a strip club near my house with a lot of contact and after touching/groping/fondling dozens of fake breasts, I can't stand them any longer.
I can't wait for the day when medical science can enlarge breasts 'naturally' without sticking foreign objects into a woman's body.