Chameleons are all different, but for the most part I would say that they are a bit more irritable when shedding. It may be stressful if it takes a long time to shed, but I wouldn't think normal shedding would cause too much stress. Some will stop eating (or not eat too much for a few days leading up to a shed) so it is important to offer some well gutloaded bugs right after a shed. I will sometimes add a little extra vitamin to his calcium depending on when the last dose was. (I have a veiled so twice a month generally for vitamins.) If your chameleon shows signs of stress, I would offer some extra privacy and just make sure he doesn't get too dried out (maybe a few extra mistings).
There is a notice-able change in behavior and mood yes. In general it's always good to leave chameleons alone and not have a lot of movement/activity around them. Remember, they're not touchy pets, whenever they shed just make sure that you mist often and that they bask enough to get the shed off as fast as possible to prevent such stress issues. Yes, I have heard that if a Chameleon sheds for too long then it's stressful and a series of mood flips and other annoying things are likely to happen.