Slate has an article on the use of exclamation points in email -- a recent email style guide suggests that we be more liberal with their use and proper writing education suggests that we keep them to a minimum.
One thing I noticed once I started actually having Hollywood types communicate with me (instead of just the other way around), was how enthusiastic they were. Everything's always great and terrific -- or GREAT and TERRIFIC!!! Your script is either "not for them" or they LOVE IT!! Even when it needs some work they still love it.
And that enthusiasm starts to infect you. I use more exclamation points than ever in emails nowadays. And I have a concern that if I use my normal method of saying that I thought a script worked well, or a movie was good, that such restrained praise will, relative to Hollywood terms, come off as damning condemnation. They'll be thinking, "damn, this guy hates everything".
That said, I do think it's worthwhile to throw a few more exclamation points in your emails. Not because, as the Slate article suggests --
Like 24-hour cable newscasters, we compensate for the unworthiness of our meanings by being emphatic!
-- that emails are unworthy of being written. But because emails are so often terse little functional things, a simple little "got it" to note that you received a package or "see you there" to say that you will show up at a function. These notes are often needed, and would just blend into a phone conversation, but in an email they can come off as cold and perhaps even hostile (my wife frets terribly when she reads a brief and functional email from a colleague, has she made them angry?!) By adding in a little ! you help clarify that you're enthusiastic, but are just keeping the email brief.