Does a Video Card hooked up to 2 monitors cut performance?

I have an ATI card with 2 DVI ports, each one with a monitor attached. When playing a game someone told me that the performance will be cut in half. Is this true?|||There will be a neligible hit on performance

I do the same to play TF2 and have IRC open on the other screen all the time|||No, the performance will not be cut in half. It will be a negligible decrease in FPS.