[quote author="Astute Observer" date=1227626495]Will it mar/damage paint? I assume it hooks on some part of the door or jam, right? How heavy can the user be? A friend of mine.... want to know if 325 lb is too much for this gadget.</blockquote>
If your friend weighs 325, pull-ups are probably a bad exercise to consider. Simply put, he is probably too heavy to do them regardless of whether he is using a home device like the one in the picture, or a (non-aided) pull-up machine in a gym.
Probably the best exercise for someone that weight to consider is walking. After taking care of the cardiovascular system, he can (and should) introduce free weights.