If you're approaching anywhere near your credit line, then you are destroying your credit score. The utilization on that card will be astronomical (I don't think it will show past 100%) and overall utilization across all lines may be very high as well (depending on the relative size of the maxed line to all of your lines).
Why would you go over a credit line? Accident? Perhaps you should get a credit increase. You may also be irresponsible with your credit use. In that case, you should think about staying away from credit cards altogether.