I do not have implants but I do have a naturally large chest (38D) and it can be really annoying sometimes. Having a barrel chest makes them look even bigger. I'm sure that my husband enjoys it <img src="i/expressions/face-icon-small-wink.gif" border="0"> but most of the time, I don't. It's too much weight on a CF chest and my back tends to hurt now and then.
I saw that someone also brought up the transplant aspect. When I saw my transplant team for the first time, they asked me if I had implants because it could be a problem during surgery if I did. When I told Dr. Budev that they were mine and not implants, she was a little shocked because most CFers have small chests.
Anyway, between the back pain a larger chest can cause, and then a possible transplant and having to have them removed, I don't think it's worth the risk.