Well...
First of all, I don't believe that Britney had any sort of breast implants... to have a job like hers (dancing, performing, etc.) implants would have more negative impacts than positive...
Second, why do people care so much about her body? It's hers and she has the right to alter it in any way. People shouldn't be so concerned about her physical appearance, eventhough it is the first thing that catches a person's attention, but also about her talent. She's an awesome dancer and an incredible singer (although, I don't agree with her lipsyncing).
I have to defend her in the fact that she's just a teeenager who's making her own decisions and should have the right to a little bit of privacy. If she chooses to disclose information about her breasts, then let her... we're not in the right to judge her for that.
That may very defensive, but I admire her and her career is what I'm striving for.