Got this from a post at Challies
Exclamation points are the most irritating of all. Look! they say, look at what I just said! How amazing is my thought! It is like being forced to watch someone else’s small child jumping up and down crazily in the center of the living room shouting to attract attention. If a sentence really has something of importance to say, something quite remarkable, it doesn’t need a mark to point it out. And if it is really, after all, a banal sentence needing more zing, the exclamation point simply emphasizes its banality!