It is the most reviled of punctuation marks. It is one I struggle with. Pundits say you should use it as little as possible. Exclamation points are to communicate only the most extreme of emotional responses.
I get that. I really do.
One teacher at first suggested that you only use a written exclamation point where one would be in actual speech. She suggested that I pay attention to my own speech and note the infrequency of exclamations.
Hmm... she didn't know me very well, because I speak in exclamations all the time! I am ALWAYS excited about something. Jazzed! Amped! Distraught! Despairing! Overwhelmed! Extremely passionate! In fact, some people have found my highly enthusiastic personality off-putting and have requested that I learn to tone it down. My true friends however learn to accept my exclamations and note their absence with a concerned 'Are you feeling ok?'
Conclusion? Our characters should be true to their own personality. If you have a hero with a larger than life personality like mine you can get away with more of the pesky punctuation. If, however, you have a wall-flower heroine you should save the exclamation points for climactic moments.