Unlike goldfish, it's highly unlikely that a VFT will ever overfeed. The traps naturally accomodate only prey of managable size, so, unless some exotic, super-nutritive bug finds it's way to your traps, it shouldn't ever be a problem. That said, it is very possible to manually overfeed a VFT, by intentionally giving it the wrong food or prey items that are too big or already decaying. Also, some bugs are just chemically unpalatable to flytraps, such as varieties of ants that produce lots of formic acid. In either case, usually the very worst is that the individual trap (and not the entire plant) will cease to function, discolor, or die. But it's not harmful to the plant - the reason there is a trap on the end of each leaf is because the plant knows that it's going to need to replace them regularly.
~Joe