Sequential Tart has an article out on How to Draw Breasts in comics, in which the author asks, "if you were trying to fight the forces of evil, wouldn't you want level nipples?" I found the story through Neilalien's levelheaded commentary on the issue. I thought I would also add a few thoughts of my own:
For the benefit of those comic readers who may not have access to this sort of information, the Champion sports bra--sometimes lovingly refered to as the "uniboob"--is the undisputed bra leader for the active female. I know of only one instance where it is not sufficient to the task, and that is in the case of fencing, where a fiberglass bra is needed. I actually quit fencing as a teenager because I could not face the ignominy of being fitted for a fiberglass bra. But back to the point: shouldn't there be at least one superheroine with a Champion sports bra?
Next, the Sequential Tart article makes the point that natural breasts are not attached to the body like two balls attached to a board. While there was once a time when we could assuredly make distinctions between natural and fake breasts, we are now so deep into the plastic surgery era that I'm not sure it makes sense anymore to insist on "the natural." It seems statistically probable that at least some superheroines would have implants.
Finally, just as Batman created his utility belt, I could see a stacked superheroine creating some sort of superbra technology. Once, while at a Star Trek convention, I heard Marina Sirtis (Deanna Troi) discuss the special bra constructed for her by the costumers at Paramount. This 24th century foundation was apparently an architectural miracle that lifted and separated even more than the Wonderbra. Other female actors at Paramount got wind of it and everyone started clamoring for this bra.